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Patent and Trademark Resource Center: Patent Search Assistance

7-Step U.S. Patent Search Strategy

The Value of a Patent Search

In order for an invention to be patented, it must be sufficiently new or different from what has already been issued or published. In patent jargon, this is called "novelty".  A thorough patent search will help an inventor assess the novelty of his or her idea. These searches are referred to as 'prior art searches.' Prior art searches may be conducted by the inventor, a patent searching company, a patent agent or a patent attorney. The PTRC will assist inventors in beginning a prior art search.

Here are some reasons why inventors should do a preliminary patent search before taking steps towards applying for a patent or hiring an attorney:

Reason 1: If the search results indicate that an idea has already been patented, then you will save the time, effort, and money involved in submitting a patent application and starting the licensing or marketing process. A product may have been patented but never have made it to the marketplace. Only 2 percent of all patents are ever commercialized. This is why inventors familiar with products or technology in a particular area may be surprised by the results of a patent search. Also the patent application fees are nonrefundable! If your application is rejected you lose the fees paid.

Reason 2: The results from the patent search may provide new inspiration and ideas for the inventor. Perhaps there is something already patented that you can improve upon. There must be novel, non-obvious improvements or changes to existing products or patents to meet the standard for a new patent. You can also refine your invention and patent application so that it does not interfere or overlap with existing patents.

Reason 3: By doing a patent search, you become more informed about the strengths of your invention and the current "state of the art," resulting in a stronger patent application or a more reasonable decision on whether to proceed with the patent process. You also become aware of companies that own patents in your area of technology. The patent search can be expanded by searching on relevant companies and looking at their full list of patents. You may decide to contact some of these companies about licensing and manufacturing your invention. You may also discover that similar inventions were not commercially viable or profitable. This may help you make a decision about whether it will be practical to continue with the patent process.

Reason 4: The search will identify patents and articles that are related to your invention. It is important to read over these to become informed about the elements required for a patent. These articles and prior patents may also comprise the list of prior art that is included with most patents.  Also if certain components of your invention have been described in detail in prior patents or articles these may be used in your application in place of detailed drawings and description that you would have to provide. This will save time and money in the preparation of your application. The knowledge from all of your searching and reading will make your patent application stronger and less vulnerable to rejection by the USPTO and challenges by other patent owners or companies.

Reason 5: If you use the services of a patent attorney, the knowledge gained from the search will help you become a more informed client. Many patent attorneys advise potential clients to perform their own preliminary patent searches, often as an attempt to "weed out" all but the most serious inquiries.

Searching for U.S. Patents on the Internet

The website of the U.S. Patent and Trademarks Office offers all the tools necessary to do a comprehensive search for previously issued U.S. patents, from 1790-present. The website contains a database of the images and drawings for all issued patents back to 1790, and keyword searchable full-text back to 1976. 

Please review the following limitations of patent searching on the Internet before proceeding with this step-by-step guide:  

  • A patent search is not an easy task to do.
    If you are an inventor who will make decisions based on the results of a patent search, it is important to consider whether you want to attempt to do a patent search yourself. A thorough search could take many hours. You may want to consider hiring a patent attorney or a patent search firm. To perform a prior art search, the following research tools should be investigated: 

    • U.S. and foreign patent databases;

    • Databases that contain journal articles and technical or government reports for the relevant subject area. You will want to utilize databases on the list of databases available statewide in Maine. These databases are made available by the Maine State Library and the Maine State Legislature;

    • Internet search engines;

    • Maine's Science, Technology and Business Portal for information on a wide variety of internet resources;

    • Company and product catalogs.

  • Searching patents that contain a specific word(s) almost guarantees that a searcher will miss several patents of interest.  Here's why:

    • You will miss patents of interest that do NOT contain your search term(s). There are many ways to describe the same product or technology. Especially searching by title is not recommended because patent titles are often very short and not descriptive. It is difficult to assemble a comprehensive list of all synonyms and keywords.

    • You will miss patents of interest that were issued before 1976. Only patents issued after 1976 are searchable by keywords from the title, abstract and entire patent. You can also not search by inventor and company name before 1976.

  • For more information on the limitations of the U.S. Patent and Trademark Office's Web Patent Database see their Important Notices page.

Patent Search Assistance

Patent and Trademark Resource Center (PTRC) staff are available to provide training on patent search processes and research tools including PubEAST, PubWEST,† and the USPTO website. Additional information is available through the USPTO website at, by phone at 1-800-786-9199, or by e-mail at For legal matters, contact an attorney or agent registered to practice before the USPTO at

Preliminary U.S. Patent Search vs. Comprehensive Prior Art Search

This guide provides a strategy for searching U.S. patents to locate and evaluate relevant prior art (earlier patents and published patent applications). A comprehensive search would also include foreign patents and non-patent literature (newspapers, magazines, dissertations, conference proceedings, and websites). PTRC staff can provide training on how to locate these additional resources.

Search Preparation and Documentation

Plan on spending a few hours learning the search process and additional hours for searching and evaluating results. The length of time depends on the complexity of the invention. Careful recording of the search process, including the databases used, date and time of search, classes searched, and patent and application numbers retrieved, is an important part of effective searching.

Brainstorm Terms Describing Your Invention

Begin by writing down a brief, accurate description of the invention. Avoid overly broad and generic terms such as "device," "process" and "system." Consider synonyms for the terms you initially select. Note important keywords and technical terms. Use the following questions to help identify keywords and concepts. 

  • What is the purpose of the invention? Is it a utilitarian device or an ornamental design?
  • Is the invention a process – a way of making something or performing a function – or is it a product?
  • What is the invention made of? What is the physical composition of the invention?
  • How is the invention used?
  • What are keywords and technical terms that describe the nature of the invention? Consult a technical dictionary or thesaurus to help find the appropriate terms.

It may be helpful to order terms according to decreasing scope. For example:
Vehicle ⇒ Automobile ⇒ Internal Combustion Engine ⇒ Fuel Injection ⇒ Injection Nozzle

Access and Review Cooperative Patent Classification Schema Using USPTO's Website Site Search Feature

The USPTO home page ( has a Site Search text box in the top right corner. CPC classification schema (class schedules) can be searching using this box.

USPTO Site Search Box

Use specific language for your search terms, such as CPC scheme umbrella. Typing in simply umbrella would be too broad and provide too many unrelated results.   

From the Search Results page, click on an entry for a Class-Subclass Scheme page. If you are not satisfied with the search results, rerun your search using synonyms you identified in Step 1 for your invention. 

Search Results ExampleScan the classification titles in the class scheme for A45B looking for the most relevant classification. Dot indents are used to show hierarchical relationships in the scheme. The more dots the more specific the concept is. Some titles may have references in parenthesis following the title that can aid in the classification selection. We find A45B 25/22 as a possible good match based on the title "Devices for increasing the resistance of umbrellas to wind." There is nothing under A45B 25/22 with two dots that is more specific, so this may be a good choice. 

Detailed view of CPC search results


Review Classification Definition Linked to the CPC Classification You Selected

If the selected classification title is underlined, it is hyperlinked to a CPC Classification Definition. CPC Classification Definitions are helpful in establishing the scope of the relevant classification and thus ensuring you have selected the most relevant classification. The definitions may include important search notes and suggestions for further searching. In this example, we click on A45B 25/22 and get the following definition, which is unusual in that it relies solely on images (most CPC definitions use text).

Definition statement for A45B 25/22

Identify Subgroups

Before retrieving full-text documents it is important to identify the most appropriate indented subgroups for each group remaining in the list. The scope of a subgroup is limited by the scope of all hierarchically higher classes and groups. In other words, the invention will only belong in a subgroup if it also belongs in all the parent classes and groups of that subgroup. (See Figure 2). It is common for an invention to belong to multiple groups or subgroups within the same class, so care should be taken to review each.

Figure 2. CPC Structure: Section, Class, Subclass, Group and Subgroup

CPC Structure: Section, Class, Subclass, Group and Subgroup

Search Issued Patents and Published Applications

Once the relevant subgroup classifications have been identified, retrieve and review all the patents from 1790 to the present and all published applications from 2001 to the present for each classification that is to be searched (see Figure 3).

Issued patents and published applications can be searched and viewed using:

  • USPTO website: Issued Patents (PatFT) and Published Applications (AppFT) at
  • PubWEST (Available at PTRC Libraries): US Patents Full-Text and US Pre-Grant Publication databases (Patent and application search can be combined and entire documents can be printed easily)

Figure 3. PatFT Search Interface

PatFT Search Interface

Review Patent and Application Documents

Review the complete claims, specifications and drawings of closely related patents and published applications. Remember, the claims constitute the boundaries of legal property rights given to the patent holder (see Figure 4).

Figure 4. Claims Section of a Patent


References & Field of Search

Check the references cited by the patent documents. Also make sure to check “Referenced By” references, i.e. recent issued patents and patent applications that cite the relevant document in hand. Take note of the additional classifications in the “Current U.S. Class,” “Current CPC Class” and “Field of Search” sections of the full-text documents. Those may lead to additional prior art not found in the first iteration of the search process (see Figure 5).

Note: the U.S. classification codes noted in “Current U.S. Class” and “Field of Search” will be phased out and replaced by CPC codes by January 2015. Refer to the original 7-Step U.S. Patent Search Strategy Guide at for instructions on searching with the U.S. Patent Classification System.

Figure 5. Cross-reference Classes, Field of Search and References Cited on a U.S. Patent

Cross-reference Classes, Field of Search and References Cited on a U.S. Patent

More Tutorials

With the transition from US Patent Classification (USPC) to Cooperative Patent Classification (CPC), many of the tutorials found online are now considered outdated. The Six-and-a-half-Step U.S. Patent Search Strategy outlined in this guide is an adaptation of the original Seven-Step U.S. Patent Search Strategy that can still be found on the Linda Hall Library of Science, Engineering and Technology's website at

The USPTO's Patent and Trademark Resource Center Program Office has created its own adaptation of the original Seven-Step Strategy that is also worthwhile. Their version still uses the USPTO's keyword index and relies on statistical mapping from USPC to CPC rather than searching CPC directly (as shown in this guide). A downloadable PDF version of their adaptation can be found at, and a video version can be viewed at


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Notes and Disclaimer

PubEAST and PubWEST are available at Patent and Trademark Resource Center libraries:

Disclaimer: The information contained in this guide is not intended as a substitute for professional legal advice. Use it as a general guide for conducting a preliminary patent search. The USPTO recommends that inventors consult a registered patent agent or attorney prior to filing an application.

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