Infringement Searching Best Practices

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An infringement search primarily requires the searcher to analyze the claims of enforceable (or “live” or “in-force”) patents, and published applications that may proceed to grant. The goal of the search is to uncover patents with claims that could represent an infringement risk to a new product, and the search should take place before the product is released to market. Infringement searches may also cover expired patent art, and sometimes non-patent sources such as product literature.

In addition to finding possible legal obstacles, infringement searches may offer some positive results. Infringement searches can sometimes be extended to include expired art, where searchers may find “safe harbor” (Freedom-to-Operate) patents which show material that has entered into the public domain. Finding expired art during the search process may allow an inventor to create, change, and/or tweak current processes of the invention to “design around” possible cases of infringement.

The common phrase used to label this type of search is not consistent throughout the industry. An infringement search can also be commonly called a clearance, Freedom-to-Operate (FTO), or right-to-use/right-to-market search; these names may each indicate a slightly different focus, and their exact meanings can vary in common usage throughout the industry. Names such as freedom-to-operate (FTO) may indicate a focus on proving certain material can be found in the public domain, while an "infringement" search can be more concerned with identifying patent claims that might cause legal trouble for a product. Regardless of the name given to the search, the best practices set forth below are generally the same.

Obstacles Facing the Searcher

The biggest obstacle for preparing an infringement search strategy is the need to understand and predict all potential generic claim language that a new product might infringe upon. To cover the necessary ground, a searcher must be able to identify technology areas and/or applications which are equivalent or analogous to the product being searched. To illustrate this point, take the following example. A product disclosure states:

"A bag closure clip including a pair of opposing T-shaped clip members held in pivotal engagement by a U-shaped metal spring. Each clip member includes a jaw, a handle, and a fulcrum. As the handles are squeezed toward each other, the jaws open to allow a bag, such as for snack food or cereal, to be inserted between the jaws. When the handles are released, the spring forces the jaws toward each other to grip the bag and hold it closed."

A quick search of the US classification system shows that US Class 24 defines subclasses for various embodiments of clips, clasps, buckles, fasteners. This is an obvious place where patents having claims that the disclosed bag closure clip may infringe upon could be found. However, this is not the only place the searcher should look. Other classes may be applicable, such as Class 132, which includes subclasses for squeeze-open clips for hair, etc; Class 223 includes clothes pins; Class 439 includes jumper cables; and Class 606 includes surgical clamps. All could potentially have devices that claim the structural elements of the disclosure.

It is also necessary to carefully evaluate the claimed material to determine whether it could possibly encompass the proposed product of interest, especially when there are any vague limitations within the claims. For example, an infringement search could be conducted on a product that has the feature of “a radio frequency identification (RFID) tag.” If a patent document is found that is related to the search subject matter, and claims an “inventory item marker,” at first glance the searcher may not think that the claim is relevant to the search. However, after reading more of the document, it might become clear that the “item marker” could be an RFID tag, as seen in the embodiments described in the specification. Thus, the claim could be interpreted as possibly including the feature of interest. (This example is used here to show how claim language should always be given its broadest possible interpretation, and any final decisions should be left to the search recipient. In general, when there is any doubt about whether a claim could possibly encompass the search subject matter, that patent should be included in the search results.)

Another major consideration in infringement searching is that each product feature should be searched separately. This is the major point in which infringement searching differs drastically from patentability and validity type searching, and failing to understand it can cause the search to become useless. To understand this point, consider a search on a product with features A, B, and C. If the searcher were conducting a patentability or validity search on a proposed claim which contained limitations A, B,and C the most damaging reference that could be found by the search is one that discloses a product with those three features in combination, essentially destroying the novelty of the item. On the other hand, if a prior art document were to claim “any device with feature A,” that document alone could not prevent someone from obtaining a patent on the three features in combination. Not so in an infringement search. In an infringement search, a patent which broadly claims even one feature is a damaging reference. Consider going to market with a new product with features A, B, and C. A patent document surfaces which broadly claims “any device with feature A.” That patent would effectively block the seller from taking his product to market unless he/she entered into a licensing agreement with the owner of the patent. Failing to do so could result in a lawsuit.

Of course, it is not always possible to search on every product feature individually. Therefore, to make the distinction between what features are common enough to be in the public domain, and which feature or combination of features might infringe on other’s intellectual property rights, it is important for the searcher to have a strong grasp of the particular technology area, and to understand the current state of the art. Open communication between the searcher and the recipient of the search results are always necessary to ensure that expectations are clear on both sides as to what the search will encompass.

Also, infringement searches are often requested to encompass unexpired (or "live" or "in-force") patents. Because the enforceability of a US patent can expire due to failure to pay maintenance fees, some searchers will be tempted to use a search product that includes US maintenance fee data to attempt to limit the search to unexpired patents only. While this would be a time-saving technique, unfortunately it is not a sound strategy because the quality of this data can only be relied upon if it comes directly from the USPTO. In addition, expired patents can sometimes be "revived," so it is often worthwhile for the search requester to be informed of any expired art that is found during the search. The general technique when conducting a clearance search is to limit the search string by publication date, usually to 20-25 years earlier than the search date. Conducting the search over the previous 25 years is recommended for safety, because it will also capture any patents with lifespan longer than 20 years due to term extensions.

Searching Patent Documents

An infringement search will usually include a search for patents and published applications from the countries in which the invention will be produced, sold, or manufactured. Many full text commercial tools will contain US and some foreign patents and published application collections.. The best selection may depend on the specific demands of the subject technology, but these tools will have coverage of US and major international country databases. Free tools such as (but not limited to) the EPO’s esp@cenet or Google Patent Search can serve as useful supplementary sources of information, such as for free patent PDF downloading.

The essential features in any full text search tool to be used for infringement searching should include:

  • Highest quality data possible/complete collections where possible
  • Timely collection updates
  • Legal status data
  • The ability to limit the search by publication country
  • The ability to limit searching to just the patent claims (only to be used if necessary)
  • The ability to limit the search by date or sort by date (only to be used if necessary)

Searching Non-Patent Literature

Non-patent sources are usually not primary sources for an infringement search. However, this type of search can include non-patent sources, especially product literature, as a means of identifying potential competitors in the market. Examining the patent holdings of close competitors is an important strategy in infringement searching, since the patented material from companies with similar products will be highly relevant to the search. Another consideration is that due to the lag between the filing and publication of a patent application, product literature may show the existence of a similar new product before its related patent applications are published.

Product literature sources that may be searched for infringement search purposes include both trade literature/trade publications, and general Internet searching. Specific collections include the collection of Thomson Gale databases (such as Thomson Gale TableBase® and Gale Group New Product Announcements Plus®), available through Dialog and associated Thomson products.

Specific Search Strategies

These search strategies are examples of specific best practices that can be applied during the course of an infringement search. These are steps to be taken in addition to accepted general search practices that apply to all searches. For a more general progression of search steps, please see the General Searching best practices article.

  • A typical infringement search will include the steps found under General Search Best Practices.
  • Scope the search to encompass all possible claimed iterations of the product. Always discuss the search strategy in-depth with a patent attorney.
  • Avoid narrowly searching for documents which only claim all or most product features; in other words, avoid falling into a patentability search mindset.
  • Perform a non-patent literature search if necessary, to identify similar products, and examine competitor’s patent portfolios.
  • Queries from full-text searches can be combined with queries from claims searches to identify patents that may claim some of the elements of the products, and describe the usage in the specification.
  • If documents are found with claims that are close to the subject matter but contain terms that appear vague or open to interpretation, the document specification may contain definitions of terms that are found in the claims. However, any document that fits this criteria should be included in the search results, and the final interpretation should be left up to a patent attorney.
  • Do not limit the search to unexpired patents ("live") and applications unless it is necessary due to time or budget restrictions. In general, it is not a good practice to limit the search to live patents by using maintenance fee data, since expired patents can sometimes be “revived.” If a date range restriction is necessary, searchers should include the previous 25 years of publications (rather than the previous 20), to take possible term extensions into account.
  • If patents of interest are found during the search, check the maintenance fee payment status and legal status to determine whether the claims are still legally enforceable. However, expired patents should still be included as part of the search results, as they can sometimes be restored to force.
  • If a US or EP published application of interest is found during the search, Public PAIR or EPOline can be used to check the status of the application. For example, the search recipient would probably like to know information such as whether the Examiner reviewed the application? Have amendments to the claims been requested/made?)


To understand the common best practices applied to the other major types of short patent searching (excluding large-scale data analysis projects), users should view the General Searching article and the Validity article.

For subject-specific searching advice, see the articles listed on the Best Practices directory page.


  1. Hunt, David, Long Nguyen, and Matthew Rodgers, (ed.). Patent Searching: Tools & Techniques. Hoboken, NJ: Wiley. 2007.
  2. Dialog Bluesheets. Dialog website, Accessed on March 26, 2009.
  3. STN Data Summary Sheets. STN website, . Accessed on March 26, 2009.
  4. Example disclosure taken from abstract of European Patent EP0841256, Accessed on October 6, 2008.

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