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Issues in Science and Technology Librarianship
Spring 2009

URLs in this document have been updated. Links enclosed in {curly brackets} have been changed. If a replacement link was located, the new URL was added and the link is active; if a new site could not be identified, the broken link was removed.

Tips from the Experts

A Short Course on Patent Reference for Science and Technology Librarians

Linda Shackle
Coordinator for Science & Engineering Services/Engineering Librarian
Noble Science & Engineering Library
Arizona State University
Tempe, Arizona

Copyright 2009, Linda Shackle. Used with permission.

Now that the full text of patents as well as patent searching tools are available for free on the Internet, every librarian who is responsible for assisting people with science and technology information should have a basic knowledge of this aspect of intellectual property. Whether a school librarian helping children discover the world of inventions, an academic librarian assisting an engineering major on a design assignment, the public librarian demonstrating how an independent inventor may do a patentability search, or a special librarian performing a patent search for the company's legal unit, patents are an integral part of the STM literature. At minimum, library staff should be able to recognize a patent citation and, depending on availability, to find the full text in one of the free patent databases on the web. Ideally, staff should be as comfortable with patents as they are with other science and engineering topics; they should know what resources to consult, and how to use those resources.

This article is an introduction to patent reference for librarians who work in U.S. libraries and will give a foundation on which to build knowledge and skills in this area. Librarians who only occasionally receive patent questions may use this as a "how-to guide" with a list of resources. Although international patents are discussed, the guide is primarily U.S.-based, and covers what a patent is, provides basic searching techniques in the major free patent databases on the web, and links to patent information sources.

Table of Contents

United States Patents …
Utility Patents
Design Patents
Plant Patents
International Patents
Kind Codes
WO & PCT applications
Parts of a Patent
Front Page
Further Reading About Patents
Searching for Patents
The Free Web Databases and Their Content
Searching for Patents by...
Assignee (corporate entity)
More on Patent Searching
Chemical Patents
Patent Classification Schemes
Prior Art (patentability searching)
Finding Other Patent Information
Citation Data
English Translations
Maintenance Payments & Expiration
The "Legal Advice" Issue
Free On-the-Web Resources Mentioned in this Guide


Patents are part of the legal area called intellectual property that also includes trademarks, trade secrets, and copyright. A patent is essentially a grant from the government, or a regional organization, giving the inventor the right to exclude others from making the invention for a specified period; as property, patents may be bought, sold, licensed, or bequeathed. The patenting process makes technological advances known to the public so improvement of the technology may occur while at the same time protecting the inventor from others manufacturing his invention. On the flip side, during the protection period consumers may have fewer options for obtaining a commodity and may pay higher prices.

Beware: The words grant and patent are interchangeable so sometimes people will refer to land grants as land patents, railroad land patents, or railroad patents; these "patents" are real estate grants, not intellectual property grants.

In order to receive a patent, the invention must be useful, novel, and non-obvious. 

United States

In the United States, there are three primary types of patents:

Utility Patents

This is the largest category of U.S. patents and encompasses processes, machines, manufacturing and composition of matter. Utility patents cover what most people think of for inventions -- mechanical, electrical, and chemical creations; however, in the U.S. this patent type now also includes such things as software programs, business methods, and gene sequences.

U.S. utility patents last for 20 years from the date of application, if the maintenance fees are paid at 3.5, 7.5 and 11.5 years. Non-payment of a maintenance fee essentially cancels the patent protection and the invention goes into the public domain early. Prior to June 8, 1995, U.S. utility patents lasted for 17 years from date of issuance; maintenance fees were required at the same intervals.

Although the first U.S. patent was issued in 1790, the patent numbering system started with patent #1 in July 1836 when the first Patent Office was formed. In December 1836, a fire consumed all of the records for the approximately 10,000 patents issued up until that time. Fewer than 3,000 of the 1790 to mid-1836 patents were restored; these patents have a numbering series in which an X is present before the number; hence their name, the "X patents."

Examples of utility patents:

Design Patents

These patents are for ornamental designs that are on manufactured items. The design may be on the surface of the item or the design may be the shape of the item itself. Design patents last for 14 years from the date of issuance.

Examples of design patents:

Plant Patents

Plant patents are for new asexually reproduced (i.e., not produced from seeds) plants. These patents last for 20 years from date of filing.

Example of a plant patent:


U.S. patent applications filed prior to November 29, 2000 were confidential and unless granted patent protection, the public never saw these applications. U.S. patent applications first went public on March 15, 2001 with the release of the Patent Applications database. Currently, inventors have the option to delay the publication of their patent application for 18 months or upon issuance, whichever comes first; if the inventor does not take the option to delay, the application is published immediately. The results of a patent application search must always be considered incomplete because of this potential 18-month delay. According to the USPTO's 2008 Annual Report, on average, patent pendency (the time from filing to issuance) is about 32 months.

The U.S. application numbering system now has two numbering series. The more recent system is usually referred to as the publication number and starts with the year followed by a seven-digit number. If the number is less than 7-digits, leading zeros should be used.


The earlier numbering system is usually referred to as the serial number and starts with a two-digit "serial code" (01=first series, 02=second series, etc.) followed by a six-digit number.


International Patents

Most countries in the world have some type of intellectual property protection, however, not all issue patents and among those that do, there are variations in the examination process and in the types of patents issued. In most countries, what the U.S. refers to as a utility patent is simply called a patent and the utility requirement (i.e., usefulness) may be called "industrial applicability."

What is patentable may also vary among countries. Patenting software is not universally accepted and designs are more commonly protected via a "registry of industrial designs" rather than issuing patents as the United States does. In some countries, the ornamentation may be copyrighted in addition to, or instead of, registering as an industrial design.

As with U.S. utility patents, patents from other countries are designated by the two-letter country code, followed by the number. To help distinguish the type of patent, and where it is in the examination process, a one-to-two character "kind code" may appear after the patent number, sometimes in parentheses. A detailed, country-by-country listing of kind codes is available from the United Nations agency, the World Intellectual Property Organization (WIPO). To coordinate with the international community and to reflect the new rule for publishing applications, the United States changed its kind codes on January 2, 2001; in addition to the WIPO listing, the USPTO also has a description of the U.S. kind codes prior to and after the 2001 change.


There is no overall patenting agency that issues an "international patent" for worldwide protection, although some regional agencies exist, such as the European Patent Office, that cover multiple countries. Consequently, inventors must file with each national and/or regional agency in which they want protection. Inventors do have the option of filing a single PCT (Patent Cooperation Treaty) application signaling their intent to patent in multiple countries. There are over 130 member countries/agencies for this treaty; the "Designated States" listing on the application indicates in which countries and/or regional agencies the inventor may be seeking protection. In the United States, the USPTO accepts PCT applications.

The PCT application's advantage is the establishment a publication filing date recognized by these 130+ countries. In most of these countries, if a dispute results from multiple inventors filing for the same invention, the patent is awarded to the "first to file," hence the necessity to establish a filing date quickly. Even if the inventor does not file a patent application in a designated country, the PCT application effectively prevents others from obtaining a patent should they file after the PCT application date. Conversely, U.S. law gives the patent to the "first to invent" frequently resulting in lengthy and expensive patent prosecutions (aka, the examination process) determining who was first.

PCT applications are given the WO two-letter country code and since 2004 are assigned a number that consists of the year followed by a six-digit number (includes leading zeros as needed). The earlier number system is WO followed by the last two digits of the year, then by a 5-6 digit number.


The Parts of a Patent

Patents can be difficult to read because they are legal documents describing technology and therefore use terminology from both the legal and technical fields. Even common English language words may have different meanings when used in patents. As an example, try deciphering the difference between "comprising," "consisting essentially of," and "consisting of" from the USPTO's glossary. Additionally, the use of generalities or generic terms avoids unnecessarily narrowing the scope of the patent, but results in seemingly odd and vague descriptions. For example, the term "plurality" is frequently used instead of specifying a number of components. A good example illustrating the strange nature of patent terminology is the Koosh ball, US 4756529, because the title (Generally Spherical Object With Floppy Filaments to Promote Sure Capture) is so far removed from how most people would describe this once ubiquitous toy.

Most modern day patents consist of four parts: the front page, drawings, specifications,and claims.

Front Page
Consider the front page of a patent to be the bibliographic data. In the U.S., the front page started to appear in selected patents in the early 1970s and by 1976 was the standard format. The amount of information on this page varies among countries; the U.S. has one of the most extensive front page formats and includes:
  • Patent number and date of issuance
  • Inventor's name
  • Inventor's address at the time of issuance
  • Assignee's name and address (if the inventor assigned the patent and informed the Patent Office of such prior to issuance)
  • Application number and date of filing
  • U.S. class(es)/subclass(es) in which this patent was placed at the time of issuance; prior to the 1970s only the primary U.S. Classification was included.
  • Number of claims

The following information is now available on the front page, but was either not included or not consistently included on pre-1970s patents:

  • The International Patent classes equivalent to the U.S. classes/subclasses in which this patent was placed
  • Field of Search: The U.S. classes/subclasses in which the patent examiner and/or inventor looked to find similar patents
  • References Cited: Related literature such as patents, books, journal articles
  • Patent Examiner's name
  • Attorney, agent or law firm representing the inventor (if the inventor employed one)
  • Abstract: A one paragraph description of the invention
  • Number of drawings in the patent
  • A single drawing representing the invention
Drawings of the invention are usually contained on a separate page or pages of the patent although some chemical patents only have structures embedded within the specifications section. Utility patents are not required to have a drawing unless necessary to explain the invention, however, most utility patents do include them. All design patents, obviously, have drawings of the design. All plant patents have "drawings" that range from either line drawings to photographs of the plant; many of these botanical drawings and photographs are in color, but they are reproduced only in black/white in the USPTO database; color copies may be obtained from the USPTO and sometimes from patent depository libraries. Prior to the introduction of the front page in the 1970s, the drawings were frequently the first page displayed for patents in the USPTO database. Some databases refer to the drawings as the Mosaics.
The specifications section is sometimes called the Description, as that is its purpose, to describe the invention. What is contained in the specifications varies according to the type of invention and may be from one page in length to 50 pages or more for some of the electrical and computer-related patents; the average length is 2-10 pages.
The claims are the most important part of the patent, as these are the legal statements describing the scope of the invention and, therefore, define what the inventor is entitled to exclude others from making. On the scanned image of a patent, the claims are usually the last section and are stated in a numerically outlined format starting with a statement similar to "I claim," "The following is claimed" or "What is claimed is."

Now that you know the contents of a patent, examine the examples listed in the Introduction section above one more time and see if you can distinguish the parts.

Further Reading About Patents

The introduction above provides enough information to recognize a patent citation or a patent document but much more information is available about patents and the patenting process. The following resources are recommended for those librarians (and their customers) who would like to know more:

Searching for Patents

The Free Web Databases and Their Content

The three main free web databases are the USPTO's Patents Issued and Patent Applications databases, Google Patents, and the European Patent Office's Worldwide database on their Esp@cenet system. Other free databases exist, each with unique features, but generally these have coverage limited to patents that are more recent.

There are two databases at this site. The Issued Patents database contains images for all available U.S. patents from 1790 to the present. For 1976 to the present, HTML full text is available and searchable. Prior to 1976, only the patent number, patent issue date, and current U.S. classification are searchable. The Issued Patent database is updated every Tuesday. The Patent Applications database became available on March 15, 2001 but contains patent applications from November 29, 2000 to the present. As inventors have the option to delay publication of their applications for 18 months, there will be some recent applications missing from the database. The Patent Applications database is updated every Thursday.

Unfortunately, the images in the USPTO databases are in TIFF and require a special plug-in for web browsers; more details are provided at Patent Full-Page Images. Depending on the TIFF viewer, in some cases, patents may only be displayed and printed one page at a time.

The European Patent Office maintains a worldwide database of patents from over 80 countries and regional patenting agencies. Coverage varies among the countries in terms of dates and availability of full text versus citation/abstract; detailed coverage tables are available. For help with deciphering these tables see explanations of country codes and kind codes. In some cases, a machine translation of the description and claims to/from English, German, French, Italian, and Spanish is offered. Update schedules vary from country to country and this information is listed in the right-hand column on the Esp@cenet home page.

Although patent images are displayed in PDF, patents over 50 pages must be displayed and printed one page at a time. For patents under 50 pages, the whole patent may be downloaded in one file.

Google Patents
Google Patents has the images for most of the US patents and patent applications however, some early X patents may be missing and the database is usually several months behind the USPTO databases. Although Google Patents has full text searching available for all patents (not just from 1976 to the present as offered by the USPTO), the searching is unreliable due to the garbled text created during OCR transfer from images into text. For this reason, Google Patents is not recommended for serious prior art/patentability searches, however, it's a fun way for students to explore the interesting world of patents.

The best use of Google Patents at this time for librarians is to obtain patent PDF images in which the whole patent may be printed/downloaded in one click.

Searching for Patents by


Have the patent number? Then it's easy to get the patent.

Google Patents In the search box put PATENT: followed by the number with no punctuation. Example: PATENT:5623411 If a patent is not found via this method, trying entering just the number.

USPTO Using the Patent Number Search in either the Issued Patents or Patent Applications database enter the number as the examples under the search box show.

Esp@cenet Click on Number Search in the left-hand column and enter the two-letter country code and the number as shown in the example to the right of the search box.


Patent databases do not have authority control for inventor names; names are recorded exactly as stated on the application; be sure to search for all variant forms of the inventor's name. As is typical with author searches, try various ways of entering difficult last names and search different spellings.

USPTO (1976 to the present) Using the Quick Search in either the Issued Patents or Patent Applications database, set the field to Inventors Name; enter the name in inverted format with a dash in between and use truncation, Smith-J$ or Smith-John$

Esp@cenet Using the Advanced Search in the Worldwide database, enter the inventor's last name in the Inventor search box. The inventor's first name may also be included, e.g., Smith John, however, this search may retrieve patents in which the two names belong to co-inventors rather than one individual. The most specific type of search uses quotation marks around the inventor's name, e.g., "Smith John"; this search retrieves only inventors that exactly match the entry without variation in content or order. To search co-inventors, enter Smith AND Harper

To limit the search to patents from a specific country, in the "Publication Number" search box, enter the two letter country code (e.g., US) with no spaces or punctuation. To limit the search to patents within a specific time frame, in the Publication Date search box enter the date(s) here in the format: YYYYMMDD.


Patent databases do not have authority control for assignee names; names are recorded exactly as stated on the application.  As is typical with corporate author searches, try all variant forms of the company name.  Be aware that patents granted to a university may be assigned to a governing board rather than to the university.  For example, many, but not all, patents that come from faculty and researchers at Arizona State University and the University of Arizona are assigned to the Arizona Board of Regents.

USPTO (1976 to the present) Using the Quick Search in either the Issued Patents or Patent Applications database, set the field to Assignee Name; enter the name with a dash in between words (use truncation "$" if desired) Minnesota-Mining$ The dash does not need to be used but is helpful in obtaining precision.

Esp@cenet Using the Advanced Search in the Worldwide database, enter the assignee's name in the Applicant's search box.


Searching for patents by subject may be the most challenging part of patent reference; however, it is essentially the same as using controlled vocabulary in indexing and abstracting services.

Patent subject searching consists of the following steps:

  1. Identify possible patent classifications for the invention by doing a keyword search and examining the results for their classification placement.
  2. Reading the definitions of the classifications found in step A to determine which are appropriate for the invention.
  3. Search by the appropriate classifications.

Note: If searching for chemical compounds, do not try using either the US or International Patent Classifications, see "Chemical Patents"

U.S. Patents Using the Quick Search, enter a word or phrase describing the subject of the invention (e.g., teeth protector). Click on the patent titles that seem appropriate and look for the Current U.S. Classification assignments (e.g., 128/861, usually in the fourth section from the top) in the text version of these patents. Go to the US Patent Classification home page and on the left side of the screen, enter a class/subclass number from your list of possible classifications into the search box. Examine the hierarchy and definition for this subclass, but also browse the schedule for the subclasses nearby -- one or more of them may also be applicable for the invention.

To see the hierarchy for this specific subclass, click on the subclass title; a new window will open and the hierarchy will be displayed.

Example: 128/861

128      SURGERY
            857      . Head or Face Protector (e.g., lips, ears, etc.)
            859      .. Oral Cavity Protectors
            861      ... Teeth Protectors (e.g., mouthpieces)

Close the hierarchy window to return to the classification schedule and click on the subclass number (ex. 861) to see the definition.

The definition describes the types of inventions covered by this class/subclass. Some definitions may also have "cross references," these are labeled "See or Search This Class, Subclass" for inventions that are in this same class but a different subclass and "See or Search Class" for inventions that are in a totally different classification.

If this class/subclass is appropriate for the invention or subject, use the browser's back button to return to the Classification Schedule. To the left of the subclass, click on the blue square with the "A" to see the patent applications published since March 15, 2001 in that category and/or click on the red square with the "P" to see the patents issued on that category.

International Patents Patents in the Esp@cenet's Worldwide Database contain International Patent Classification (IPC) numbers and may be used to find patents from different countries and written in different languages but are about the same subject. The IPC uses a hierarchical outline of all possible subject categories for inventions; it is similar in concept to the US Classification system but has a different format.

Subject searching for international patents consists of the same process as the U.S. patents:

  1. Identifying possible patent classifications for the invention. 
  2. Reading the definitions of those classifications to determine which are appropriate for the invention.
  3. Search by those classifications. 

Select "Quick Search" from the column on the left, enter a word or phrase in the third search box. Be sure to keep the database set to "Worldwide" and the type of search to "Words in title and abstract." Make note of the IPC/International classifications for patents of interest.

Searches by keyword are limited to patent title and abstracts; full-text searching is not available even if the patent is available in the database in full text. A worldwide search (i.e., not limited to a specific country) will only process the first two words entered in the search box; however, a search limited to a specific country will process up to five words in the "Title or Abstract" search box.

Go to the IPC and click on the "Browse and Search the IPC" link; in the left column, in the "Current Symbol" box, enter the IPC classification (e.g., A61C 5/14). For words within the IPC hierarchical outline that are highlighted in blue, click on the word to see its definition.

When you have found the appropriate International Patent Classification(s), click on the little "magnifying glass" icon that is located to the left of the classification code. The "IPC Bridge" window will appear in the middle of your screen; in the "Patent Databases" section of the IPC Bridge window, click on the "Esp@cenet (AL)" link that will automatically do a search for that classification in Esp@cenet.

More on Patent Searching

Chemical Patents

For those who are "chemistry-challenged" or "chemistry-phobic," for your own peace of mind, please skip this section! This is the only section of the guide that will mention fee-based resources.

Chemical patents present unique searching challenges and require knowledge of college-level chemistry for both inorganic and organic. The challenges result from how the patent classification systems categorize chemicals and the use of Markush structures in patents.

The chemical sections of patent classification systems revolve around the elemental components, position within the periodic table, structure, and material category (e.g., ceramics, paints, vegetable oil). Classifications are complicated and don't provide access to patents in a way most chemical and pharmaceutical researchers need, so searching by classification for chemicals is not being covered in this article.

Markush structures provide a short hand way to describe multiple, structurally-related compounds with a single structure diagram, followed by statements describing what elements or molecules could be substituted at different points in the structure. Although very convenient for the inventor, Markush structures present enormous problems for database indexers and for patent examiners and searchers trying to decide if a patent covers the compound or synthesis under investigation. A single Markush structure may represent hundreds of different compounds, some of which may not even be discovered until many years after the patent issues. For example, examine the claims section of this patent, US 5741892; how many compounds do you think are covered by these claims? Next, check out how Chemical Abstracts Service (see 1998:102892 or CAN 128:167719) handled the indexing of this patent; CAS does not try to identify all the hypothetical variants.

Consequently, patentability searching for a newly synthesized compound is complicated and should be left to the professionals who have the required specialized knowledge along with specialized databases. On the other hand, patents for existing compounds, especially pharmaceuticals, may be easier to find.

The FDA's Electronic Orange Book links pharmaceuticals still under patent back to the actual patent. Patents for well-known substances may be listed as preparation/synthesis references in such basic chemical reference works as "Merck Index," "Combined Chemical Dictionary," and the "Kirk-Othmer Encyclopedia of Chemical Technology." Use Chemical Abstracts/SciFinder to find chemical patents by structure/substructure and by name, CAS registry number, or molecular formula (limit the document type to patents for large search results).

Patent Classification Schemes

The USPTO has a hierarchical outline of all possible subject categories for inventions called the U.S. Manual of Patent Classification; all issued patents and patent applications are assigned to one or more of these categories. The classification system uses a two-segment number, such as 128/861, in which the first number indicates the main category or "class" and the second number is the subcategory or "subclass." 128/861 is the category for "teeth protectors, such as mouthpieces." The hierarchy of 128/861 is outlined as follows:

    857  . Head or Face Protector (e.g., lips, ears, etc.)
    859  .. Oral Cavity Protectors
    861  ... Teeth Protectors (e.g., mouthpieces)

128 is the main class.

CAPITAL LETTERS signify a division of the main class (in this case, subclass 846 which is for Body Protecting or Restraining Devices).
A single dot signifies a subdivision of the division (in this case, subclass 857, which is a subdivision of subclass 846, which in turn is a division of class 128)
Two dots signify a subdivision of a subdivision (in this case, subclass 859, which is a subdivision of subclass 857, which is a subdivision of subclass 846, which is a division of class 128)
And so on...

Patents are placed in the most specific subclass related to the invention. The US Patent Classification system was designed long before computerized databases so there are no leading zeros and other devices in use to keep things organized. Additionally whole sections have been moved with their old numbering systems intact into other areas so that the subclasses within a class do not necessarily fall in numerical order. Consequently, although the system is hierarchical in nature, you cannot search a broader class and get all the patents assigned to the subclasses indented under that. For the teeth protector example above, searching for 128/846 will only find those patents placed in the 846 class (i.e., those patents that do not fit in the more specific classes underneath) and will not find the patents placed in the classes indented underneath it (ex., 128/857, 128/859, 128/861). Truncation may be used in USPTO databases (ex., 128/8$) but be sure you fully understand how the subclasses are arranged in a particular class and how that will affect the results.

The International Patent Classification (IPC) system is more modern although less detailed than the U.S. Classification System and lends itself easily to truncation. For the teeth protector example, the hierarchy looks like this:

A                     Human Necessities
A61                 Medical or Veterinary Science; Hygiene
A61C              Dentistry; Apparatus or Methods for Oral or Dental Hygiene
A61C5/00       Filling or Capping Teeth
A61C5/14       Lip or mouth protectors

All modern patents are assigned International Patent Classifications; modern U.S. patents are assigned both International and U.S. classes.

As with patents themselves, the patent classification systems use terminology that can be confusing to the consumer. The classification systems are geared toward what the invention is and what it does, but not necessarily what it's used for. A bicycle seat would mostly likely be classed in 297/195.1+ (the + indicates that all the subclasses indented underneath are possibilities); this is the category for straddle seats, which could be used in other applications besides bicycles. An air-conditioner is used for cooling buildings, but what an air conditioner does is called heat exchange by engineers, so class 165 is a likely area where these types of inventions would be placed.

If you're thinking that only an engineer would know that, you're right, and that's why librarians may instruct and demonstrate how to use the classification tools, but they do not interpret the systems for others nor recommend specific classes to search. (See the "Legal Advice Issue" for more cautions.)

Prior Art Searches

Individuals who wish to apply for a patent must check to see if the invention already exists; this is called a prior art search or a patentability search. In this case, "art" does not refer to a drawing or other visual representation of the invention but rather to the existing knowledge or creations within a field. A prior art search not only includes searching the patent databases by subject (as described above) but also searching:

Individuals should do their own prior art searching before hiring a patent attorney or agent. If prior art is found, the individual may reconsider applying, thereby saving both attorney and application fees, or the individual may still seek the advice of an attorney as to whether the found art is indeed his/her invention in either whole or part. Even if an individual does a prior art search and finds nothing, the patent attorney/agent will likely charge for a prior art search performed by a professional patent searching agency.

Finding More Patent Information


An assignee is an individual or organization to which the inventor has transferred the patent rights. An inventor may sell or give a patent to another individual or company and this individual or company becomes the assignee. If an individual works for an organization and discovers an invention on company time, the individual will be listed on the patent application (and eventually the granted patent) as the inventor and the organization for which he works will be listed as the assignee. If an assignee for the invention exists at the time of issuance, this will be recorded on the patent. Once the patent issues, if the inventor or assignee notifies the USPTO, changes in assignment may be found in the Assignments Database.

Citation Data

Of course, you can use subscription sources such as "Web of Science" to find citation data, however, free resources are available.

Esp@cenet To see if a patent has been cited by other patents:
  • In the left column, click on patent number search
  • Keep the database selection set to "Worldwide"
  • Put the patent number in the patent number box (if necessary, include the two letter country code immediately before the number if too many results are retrieved from a plain number search)
  • On the results list, click on the title of the patent to display the bibliographic data screen
  • On the bibliographic data screen, click on the red "View list of citing documents" which should be near the middle of the screen.
Google Patents Enter in the number (you may want to search the number both with and without the two letter country code). If you entered a number for a U.S. patent, the first item in the list is usually the patent itself. The others in the list are U.S. patents that cite your patent. To get the count you have to go to the last page of the results and see what the number is.
Google Scholar To see if a patent has been cited within the text or references of an online journal article, enter in the number (you may want to search the number both with and without the two letter country code).
U.S. Issued Patents Database The USPTO's Issued Patents database has citation data that is searchable from 1976 to the present.
  1. To determine how many times a U.S. patent has been cited by another U.S. Patent:
    Using the Quick Search:
    • Enter the number of the patent (example: 6404950) in the first search box and change the field from "All Fields" to "Referenced By"
  2. To determine how many times a foreign patent has been cited by a U.S. Patent:
    Using the Quick Search:
    • Enter the foreign patent number in the first search box and change the field from "All Fields" to "Foreign References"
    • Be Aware: The way foreign patents are cited is not consistent -- you'll need to search several variations including with and without the country code before the number and with variant spacing and punctuation --- be creative!
  3. To determine how many times a non-patent publication has been cited by a U.S. Patent:
    Using the Quick Search:
    • Enter in the first author's last name in the first search box and change the field from "All fields" to "Other References"
    • If the author's last name is too common, return to the Quick Search interface and use the second search box to include a word/abbreviation from the journal title (or title of the book or conference); change from "All fields" to "Other References"  (Example: chemical or chem)

English Translations

Patents are written in the language of the country in which they are issued, so inevitably when dealing with international patents you'll be asked if an English translation exists. The answer is "Maybe." The only way to get a precise, word for word translation, is to hire a firm specializing in patent translations, an expensive and not always viable option; but for the individual, especially a student, who only needs to get a general idea of what the patent covers, Esp@cenet may be helpful.

When looking at the bibliographic page for a patent in Esp@cenet, there will frequently be a column on the right of the gray box labeled "Also Published As." These are the "equivalent patents" that have been filed, or issued, in other countries for this invention. Obviously, you should look for an equivalent patent from the U.S. (or another English speaking country). Note that these are not necessarily word-for-word translations and differences in the claims may exist due to patent law unique to a specific country.

Another option is Esp@cenet's free machine translation service. The services translates the full text of French, German, Italian, and Spanish patents into English; but beware, you get what you pay for here. The translations are at best rough, and at times, downright hilarious or indecipherable. To find the translation service, click on the Description tab for the patent; a yellow "Translate this text" link is in the upper right of the gray box, if available.

Maintenance Payments & Expiration Dates

Although U.S. utility patents last for 20 years from date of application, some of these patents expire early while some have their terms extended beyond the original 20 years.

Early Expiration

To keep a U.S. utility patent in force for its full term, the inventor (or assignee) must pay maintenance fees at 3.5, 7.5, and 11.5 years. Failure to pay results is an abandonment of the patent; the patent expires early and the invention goes into the public domain; once in the public domain, others have the right to manufacture the invention.

To determine the status of a patent's maintenance fees or to determine if a patent has expired for lack of maintenance fee payment:

Term Extensions

Some utility patents involve material needing Food and Drug Administration (FDA) approval before marketing. FDA approval for food additives, pharmaceuticals intended for humans and even some medical devices may take years and could adversely affect the length of market exclusivity. In these cases, inventors/assignees may request a term extension. In addition to PAIR (under the Patent Term Adjustments tab), other resources to use to check for term extensions are:


Patent statistics help measure the industrial and economic activity of a country or state.

The USPTO statistics are organized by inventor's state of residence, assignee name and broad technology categories. If you use the USPTO databases to gather statistics, for example how many patents were issued in Arizona in 2003, the number retrieved will be larger than that listed in the USPTO statistics. The USPTO only considers the place of residence of the first inventor for gathering statistics, while a database search cannot distinguish between first and second co-inventors. Consequently, a patent co-invented by two individuals, the first living in California and the second in Arizona, would be counted as belonging only to California in the USPTO statistics, but in the USPTO databases, that patent would be retrieved by either a California or Arizona search. Another caution is that many of the USPTO patent statistical tables are counting only utility patents and not design or plant patents.

For international patent statistics, check out:

And Finally...The Legal Advice Issue

As with all legal topics, you must avoid giving legal advice during the patent reference transaction but still be helpful in connecting the individual with the needed information. "Instruct, demonstrate, but never interpret" is the guiding principle.

Start prior art/patentability searching transactions, explaining what you can and cannot do for the individual; put a positive spin on it. Example: "Although I can't give you legal advice, I am able to show you how to use the patent databases."

Be prepared to give information for where individuals may get help, such as:

Have a previously prepared demonstration available on how to search the patent databases using keywords and classification; select a simple invention for this demonstration -- something that every person would understand. Stick to strictly showing the steps without interpretation. Do not use the individual's invention as the demonstration example no matter how much he may cajole or insist; if you use his invention, you'll almost always find yourself stepping over the interpretation line by suggesting terminology and classifications for searching, in essence giving legal advice on the "field of search."

Yes, this is antithetical to what reference librarians do and certainly doesn't sound like good customer service but the results of the prior art search will be what the individual uses to decide whether to apply for a patent himself, employ a patent attorney, or decide not to patent. Time, money and business plans ride on this decision. If the individual feels he is not capable of doing his own prior art search, direct him to someone who can -- the patent attorney or agent.

The ultimate caution is never do a prior art search for an inventor whether on or off the job and if asked, you can't recommend a student who can be hired on the cheap to do this either. Direct the inventor to the Patent Attorneys and Agents database.

Of course, if you are helping a student with an assignment, and the student does not intend to go forward with a patent application, you may loosen up on all of these legal cautions. Consider the transaction as an instruction opportunity and help the student with suggested keywords and classifications; but at appropriate points in the transaction remind him that in "real life," he would be getting a patent attorney to assist him. If the student is planning to file a patent application, advise him to talk with his instructor so the appropriate unit in your college/university starts assisting the student as soon as possible to avoid legal pitfalls. For example, some graduate students may need to delay publication of their theses/dissertations in order to meet patenting requirements.

You may also wish to consult the web sites of the Patent and Trademark Depository Libraries to see how they handle the legal aspects of patent searching and what wording they use.

Free On-the-Web Resources Mentioned in this Guide:

Electronic Orange Book
This database from the U.S. Food and Drug Administration (FDA) contains patent information for drugs; the propriety name (i.e., trade name) search is preferred. May be helpful in finding patents describing the synthesis of modern drugs or for determining if patents are still in effect and/or have been extended.
A worldwide patent database developed and maintained by the European Patent Office and containing patent information for over 80 countries and patenting agencies. This is not a complete database of all the world's patents as dates of coverage varies among countries and some countries' patents are available in full text, while others only have bibliographic information plus an abstract.
Google Patents
Useful for finding a copy of a U.S. patent in PDF with all the pages in one file. Word searching is too unreliable to be used for serious patentability searching, but may be fun for younger students.
USPTO: Assignment Database
Use to determine if an inventor has transferred his patent rights to another individual or company (assignees).
USPTO: Issued Patents and Patent Application Databases
There are two databases at this site. The Issued Patents database contains images for all available U.S. patents from 1790 to the present. For 1976 to the present, HTML full text is available and searchable. Prior to 1976, only the patent number, patent issue date and current U.S. classification are searchable. The Issued Patent database is updated every Tuesday. The Patent Applications database became available on March 15, 2001 but contains patent applications from November 29, 2000 to the present. As inventors have the option to delay publication of their applications for 18 months, there will be some recent applications missing from the database. The Patent Applications database is updated every Thursday.

Unfortunately, the images in the USPTO databases are in TIFF and require a special plug-in for web browsers; more details are provided at Patent Full-Page Images . Depending on the TIFF viewer, in some cases, patents may only be displayed and printed one page at a time.

USPTO: Kind Codes
Kind codes are one or two character designations following the patent number and indicate what type of patent it is and/or at what point it is in the patenting process. This list is only for U.S. kind codes.
USPTO: List of Patent and Trademark Libraries
Approximately 80 libraries are in the U.S. in the PTDL program; some of these libraries provide patent information and searching instructions on their web sites. You may also contact these libraries for help with your customers' specific patent questions. Some PTDLs provide outreach programs; ask if they will do a workshop in your area for librarians and/or independent inventors.
USPTO: Patent Application Information Retrieval (PAIR) database
For recent patents and applications, this database tells what actions have been taken and provides copies of the documentation. Useful for determining if a patent has expired early from non-payment of maintenance fees.
USPTO: Patent Attorney/Agent Search
The database of attorneys and agents licensed to practice before the USPTO; these are people who have passed the Patent Bar Exam.

A patent attorney has a law degree and has passed both a traditional bar exam for their jurisdiction as well as the Patent Bar Exam. This type of attorney may represent an individual in U.S. Court for patent litigation in addition to assisting with filing for a patent and communicating with patent examiners during patent prosecution. A patent agent usually has one or more advanced science or technology degrees in addition to passing the Patent Bar Exam; an agent may assist an individual with filing for a patent and communicating with patent examiners during patent prosecution but may not represent the individual in U.S. Court. Do not direct customers to regular civil or criminal lawyers for intellectual property matters.

Not every attorney or agent listed in this database is available for the public to hire. Those listing a corporation (e.g., Motorola) as their "firm" are employees of that business; instead direct the individual to look for attorneys and agents who either work for a law firm or are in business for themselves.

USPTO: US Patent Classification
Portal to the US Patent Classification system. Includes a concordance between the US system and the International Patent Classification (IPC).
USPTO: Patent Terms Extended
A listing of drugs, food additives and medical devices whose patent terms were extended because FDA approval delayed marketing of the product.
WIPO: International Kind Codes
Kind codes are one or two character designations following the patent number and indicate what type of patent it is and/or at what point it is in the patenting process. This list is covers kind codes for over 50 countries.
WIPO: International Patent Classification
Portal to the International Patent Classification (IPC).
WIPO: World Patent Report
A review of current international patenting activities with statistical data.

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