A patent search verifies that an invention is original by checking patent databases for a similar invention before the inventor spends time and thousands of dollars applying for a patent. The United States Patent and Trademark Office (USPTO) will reject a patent application if a valid patent already exists for the same invention.

Some entrepreneurs may try to do their own patent search to avoid spending money on hiring an organization that performs patent searches.

However, inventors should be aware of potential problems before conducting a patent search. These include:

  • Searching for patents is very difficult. Inventors commonly fail to find patents that a professional patent search organization or patent attorney would discover. The search is only as good as the keywords entered, and without experience, inventors often won't enter the optimal keywords. Most patent descriptions are also represented by drawings which are not searchable using keywords.

  • The patent collections of most websites are also limited. For example, the USPTO website doesn't show full-text patents issued before 1976. This won't concern people working in high-tech fields, but may be a serious limitation for someone with a more traditional invention.

Patent attorneys typically suggest that conducting your own patent search is a good first step, but additional measures should be taken to confirm whether a valid patent already exists.

The following steps will yield the most productive results in your patent search:

  1. Brainstorm terms or phrases. Choose a term that might appear in the patent description, such as "insulating beverage container," and type it into the search box of your chosen patent search engine.

  2. Search for patent classifications. The USPTO search is considered the best place to start. In the search box at the top right of the USPTO homepage, enter in quotes CPC Scheme (Cooperative Patent Classifications) and your chosen keywords.

  3. Browse relevant results. The Patents Full-Text and Image (PatFT) database will help you find the most relevant classifications for your information. Check their relevancy using the CPC Classification Definition which is often linked to your results.

  4. Get the right number of results. If the search returns too many results, try searching for different terms from your brainstorming list or refining the search using advanced search functions. If it doesn't return any search results at all, use different terms from your brainstorming list or synonyms. The International Patent Classification Catchword Index can be useful if you still aren't getting results.

  5. Assess the patents. Once you have a manageable number of results, click on the listed patents with your selected CPC classification and compare them to your own invention. Review them and decide which are the most relevant by scanning the abstracts and representative drawings on the front page. Note the numbers and Cooperative Patent Classifications of the most similar inventions. It's smart to repeat the process using a variety of keywords to get the most complete picture.

  6. Evaluate the patents more closely. Once you have a selection of the most relevant patents, take a more in-depth look at them. Note any similarities to your own invention. Focus on the additional drawings pages, specifications, and claims. Also note the references, as they may lead you to other relevant patents.

  7. Conduct further searches. Repeat your CPC classification search using the Applications Full-Text and Image AppFT database. Then widen your search to use keywords without classifications in the PatFT and AppFT databases and perform classification and keyword searches on the other websites and resources listed above.

  8. Look to different websites. Using a variety of online sources at the same time can be helpful. The strengths of several websites will complement one another, making the search process easier.

A number of credible resources can help people in their patent search. These include:

  • The USPTO's Patents Full-Text and Image search page: This should be the first stop for anyone conducting a patent search. The site offers an intuitive search function and helpful guide to educate inventors on its features. However, its online search will not show full-text patents issued before 1976.

  • Free Patents Online: This free, fast-loading site provides copies of patent documents in PDF form. This helps users view the illustrations contained within patent application more easily than searching through the USPTO.

  • The Global Patent Network: This is an initiative between the USPTO and State Intellectual Property Office of the People's Republic of China. Its database includes full-text Chinese patents, English translations, and complete document images.

  • European Patent Office's Worldwide Espacenet patent database: This is another valuable international resource.

  • Other International Property Offices: Official bodies in several countries, including Australia, Canada, France, Great Britain, Israel, and Taiwan, also have searchable databases.

  • Google Patent Search: This Google website is very fast, with a database that stretches back further than the USPTO's online search and Free Patents Online. It has a relatively small number of search fields though which limits its search capabilities and also doesn't always feature the most recent patents.

  • Patent Application Information Retrieval (PAIR) system: IP customers can use this system to easily and securely retrieve and download information about patent applications and their statuses.

  • The Patent Official Gazette: Inventors can also browse through patents issued within the week in the electronic version of this publication. Users can search new patents by their classification or type (utility, design, or plant). This is an excellent source for up-to-date information often overlooked by other patent databases.

  • Common Citation Document application: This website application is another good source of up-to-date citation information regarding patent applications. It consolidates information from all five participating intellectual property (IP5) offices so you see all results for the same invention produced by various offices on one page.

  • Publication Site for Issued and Published Sequences: This website has sequence listings, tables, and other mega items for granted United States patents and published United States patent applications. Access the relevant document detail page and then submit a sequence identification number or mega table identification number to see all sequences and tables for listed patents and publications.

  • Patent Assignment Search: This website has a searchable database of patent assignments and ownership changes.

  • The USPTO Public Search Facility in Alexandria, Virginia, and local Patent and Trademark Resource Centers: These brick-and-mortar facilities let you search through patents online, in print, and on microfilm. They also have staff that may be able to assist in your search or train you in the best patent searching techniques.

Common Abbreviations Used in Patent Searching

A number of abbreviations are commonly used in the area of patent searching. Understanding the most common will help you in your own searching. These are:

  • AADR: assignee address (complete string)

  • ABST: abstract

  • AC: assignee city

  • ACLM: claims

  • ACN: assignee country

  • AGTC: agent address city

  • AGTCN: agent country

  • AGTN: agent name

  • AN: assignee name

  • AGT: agent

  • APD: filing date

  • APN: application number

  • CCL: U.S. class

  • AS: assignee state

  • ASEX: assistant examiner name

  • DN: document number (also PN, meaning patent number)

  • ECLA: ECLA classification

  • FOS: field of search

  • FREF or FREFN: foreign patent reference

  • IADR: inventor address

  • IC: inventor city

  • ICN: inventor country

  • IN: inventor name

  • IPC: IPC classification

  • IPCR: revised IPC classification

  • IS: inventor state (within the U.S.)

  • ISD: publication date

  • KCOD: Kind code

  • OREF: other references

  • PARN: parent case

  • PCCL: primary class

  • PD: publication date

  • PEX: primary examiner name

  • PRICN: priority country

  • PRIN: priority number

  • PRIR: foreign priority

  • PT: document type

  • REF or REFN: U.S. patent reference

  • SPEC: specification

  • TTL: title

Frequently Asked Questions

  • How do you read a patent?

Local patents have a clear format with sections identified by numbers in parentheses known as INID codes. These codes help you understand the information you're looking at:

Type of document. This will usually read United States Patent, United States Design Patent, or United States Plant Patent. In some cases, the heading may be Patent Application Publication, Reissued Patent, Defensive Publication, or Statutory Invention Registration. The last name of the inventor is usually printed underneath this. If this invention has more than one inventor, the last name of the first is printed, followed by "et. al."

Patent number. Some have a number only, while others have one of the following letter codes:

  • AI: additional improvement patents, issued between 1838 and 1861
  • B: re-examination certificate, denotes a patent was issued and examined again at the patentee's request. Also used in the mid-1970s for documents published in the Trial Voluntary Protest Program
  • D or Des.: design patent, covers the look of a functional object
  • H: statutory invention registration, published between 1985 and 2013
  • NP: non-patent literature, not published by USPTO
  • PP or Plt.: plant patent
  • RE: reissue patent
  • RD: reissued design patent
  • RP: reissued plant patent
  • T: defensive publication, issued between November 5, 1968 and May 5, 1987
  • X: issued before 1836 when patents weren't numbered

Documents also have a letter after the patent number. These appear on the patent's face after January 2, 2001. The codes may feature on some patents issued earlier in some databases. These letter codes are as follows:

  • A1: published patent application (A2 for second publication, A3 for third, etc.) or patent issued before 2001
  • A9: corrected published patent application
  • B1: utility patent, never published before or re-examination certificate issued before 2001
  • B2: utility patent, published previously as an application
  • C1: re-examination certificate (C2 for second re-examination certificate etc.)
  • E1: re-issue patent
  • F1: re-examination certificate of re-issued patent (F2 for second re-examination certificate of re-issued patent etc.)
  • H: statutory invention registration
  • I1: X patent
  • I2: re-issued X patent
  • I3: additional improvement patent
  • I4: defensive publication (T series)
  • I5: trial voluntary protest program documents
  • P1: plant patent issued before 2001 or plant patent application published after January 2, 2001 (P4, P5 for additional publications of this type)
  • P2: issued plant patent without pre-grant publication issued after January 2, 2001
  • P3: issued plant patent which was published previously issued after January 2, 2001
  • S: design patent
  • X6: post-issue patent document, such as a dedication, a disclaimer, or a certificate of correction
  • X7: patent assignment
  • Date of patent's issue by USPTO.
  • Title of patent. These were fairly vague on early patents, but more recent patents have more specific titles.
  • Names of all inventors. These names are usually listed with their cities or even complete addresses.
  • Assignee. This is the company or individual that owns the patent if it isn't owned by the inventor.
  • Term extension notice. This term is expressed in days.
  • Application number. This is a six-digit number assigned sequentially.
  • Filing date. This is the date the application was filed, not necessarily the first U.S. filing date.
  • Prior publication date. This is noted if the patent was published while approval was pending.
  • Related U.S. application data. This is the ID number of any related local applications or patents.
  • Related foreign priority data. This is the ID number of any related international applications or patents.
  • International Patent Classification. This refers to the patent's subject matter.
  • United States Patent Classification. This code is either a USPC (used before December 2014) or CPC.
  • Field of search. These are the U.S. classes or subclasses the examiner searched when assessing the patent.
  • References cited. These citations are either prior art found by the examiner or listed by the patentee on an Information Disclosure Statement.
  • List of primary and assistant examiners. These are not denoted by an INID code.
  • Attorney, agent, or firm. These are any legal representatives that filed and prosecuted the application.
  • Abstract. This is a short summary of the invention, usually less than 150 words
  • Number of claims and drawing sheets. This is not denoted by an INID code
  • Representative drawing, chosen by the examiner. This is not denoted by an INID code.
  • How do you know whether a patent is enforceable?

Patents are enforceable from their issue date for a specific term unless it expires earlier. Once a patent has expired, it is no longer enforceable. The USPTO website offers a patent term calculator which can help you determine whether a patent is still enforceable. Make sure to assess the text-based display and PDF patent image. You can also search for the patent in another search of your choice, like the European Patent Office's espacenet system or Google Patents.

Look for the following indicators that suggest whether a patent is valid or expired:

  • An original-issue utility patent number under 5,000,000. All these patents expired before August 31, 2010. Patents with higher numbers require more verification.

  • A provisional patent was converted to a utility patent. In rare cases, applicants convert provisional patent applications to utility applications instead of starting a new application. In these cases, the term commences from the provisional filing date. Some patents expire sooner than usual due to earlier-issued patents on the same invention.

    When two applications claim the same invention, a terminal disclaimer applies. The USPTO's Public PAIR system displays terminal disclaimers in the image file wrapper. PAIR's continuity tab may show this information for patents too old for an image file wrapper. Once you know which patent the terminal disclaimer came from, you can evaluate when the term was disclaimed. A terminal disclaimer might state that the patent is valid for the full statutory term of the earliest patent, a specific date, or a combination of the two.

  • An extension due to USPTO delays. Patents from applications filed on or after May 29, 2000 may have these extensions. Known as patent term adjustments, these are usually flagged on the patent with an asterisk in parentheses.

  • An extension that doesn't concern the USPTO. In rare cases, patent terms are extended after extreme delays in government approvals that don't concern the USPTO. Pharmaceuticals, food products, and medical devices are most commonly granted these extensions, as U.S. Food and Drug Administration approval can cause delays.

    While it hasn't occurred since the late 1980s, Congress can also extend patent terms. No current patents are subject to these extensions at the time of writing, but it could happen in future.

  • A re-examination certificate that shows claims were lost. The USPTO database also presents re-examination certificates attached to its patent images. These will show whether some or all of the claims were lost when the patent was re-examined. Patents are occasionally withdrawn on the order of the Commissioner of Patents, but when they do they are also usually removed from the USPTO database.

  • Unpaid maintenance fees showing in USPTO PAIR system. Modern utility patents expire if their maintenance fees are unpaid. These fees are due at 3.5 years, 7.5 years, and 11.5 years. Inventors may pay the fees six months before they're due. There is a grace period of six months after the due date, after which an unmaintained patent becomes invalid. An expired patent can be revived within the patent's term if the payment delay was unintentional.

    The USPTO PAIR system shows whether maintenance fees are current. Simply search for the patent, click on the fees tab, then select "Maintenance Fees – Retrieve Fees to Pay."

    If the maintenance fee due dates are in the future, then the patent is still current. If the maintenance fee due dates are six months ago or less, then the patent is in the grace period. When the maintenance fee due date is more than six months ago, the patent has expired, but may be revived.

    Patents based on applications filed before December 1980 did not require maintenance fees, but they have all expired. Plant and design patents do not require maintenance fees.

  • A patent is invalid. Courts can declare patents invalid, but there is no easy way to determine whether this has occurred. You may find the patent number searching through the Lexis, Westlaw, or BNA USPQ databases of court records. With a case citation, you can search for the case in the Public Access to Court Electronic Records system. Sometimes a Google search for the patent number will also reveal court cases.

    If you are unsure whether a patent is still valid, patent attorneys can conduct validity studies and offer their advice.

Searching for patents can be difficult, but it can also provide enough information to help you feel confident in the originality of your ideas and your right to pursue a patent for them. If you need help with your patent search, you can post your question or concern on UpCounsel's marketplace. UpCounsel accepts only the top 5 percent of lawyers to its site. Lawyers on UpCounsel come from law schools such as Harvard Law and Yale Law and average 14 years of legal experience, including work with or on behalf of companies like Google, Menlo Ventures, and Airbnb.