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Patent Validity and Invalidity Search: A Beginner's Guide

Patent validity or invalidity searches can be valuable tools in various stages of the IP lifecycle. Learn more about the process, the various use cases, and why it should form part of your IP strategy in this comprehensive guide.

Patents are an essential aspect of intellectual property protection, granting inventors exclusive rights to control the production, usage, and sale of their inventions. However, a patent does not guarantee protection, as they can still face challenges to their validity, subjecting patent holders to potential legal risks.

In order to mitigate these risks, a patent validity or invalidity search may be conducted. Performed in different stages of the IP lifecycle, both searches evaluate the strength and validity of a patent, offering valuable insights into its enforceability and potential vulnerabilities.

In this guide, we’ll explore the basics of a patent validity or invalidity search, the various use cases, how they are conducted, and their role in your IP strategy.

A patent validity or patent invalidity search is a type of prior art search that identifies references that may disclose the novel and inventive features claimed by a granted patent. The goal of this search is to find prior art that was not considered during the patent examination process, which could potentially invalidate the claims of a patent.

What is the difference between a patent validity and a patent invalidity search?

Both patent validity and patent invalidity searches look for prior art. These terms may have been used interchangeably, but the key difference is the purpose of the search.

A patent invalidity search may be conducted in aid of patent litigation, to check the quality of a patent portfolio, or to challenge the validity of a competitor’s granted patents. Also called an opposition search, in the context of a lawsuit defendants attempt to “kill” the patent of interest (specifically its claims) by presenting prior art.

On the other hand, a  patent validity search is typically conducted from the perspective of someone seeking to enforce or defend a patent. The goal is to assess the strength of the patent’s claims and ensure that it can withstand challenges in court or other proceedings.

Though there are key differences in their focus and objectives, both searches involve a comprehensive examination of prior art and other relevant information to evaluate the strength and validity of a patent. 

What is prior art?

In the U.S., the legal definition of prior art is set out in 35 U.S.C. § 102, which defines prior art as “a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention.”

Prior art may include patent and non-patent literature (scientific journals, websites, product manuals, videos, standards, etc.) published before the effective date of the patent of interest.

What types of prior art are considered in a patent validity search?

Prior art in a patent validity and invalidity seearch

1. Patent and patent applications

Prior patents and patent applications are a valuable source of prior art for invalidity searches. Patents that were filed before the challenged patent and have similar or identical claims can be used to show that the invention was not novel or non-obvious at the time the challenged patent was filed.

2. Non-patent literature

This includes academic papers, conference proceedings, technical reports, electronic or internet publications, magazine and newspaper articles, websites.

3. Applicant's Admissions of Prior Art

These are the declared known arts of the patent applicant and are included in the background of the patent specification.

4. Public use or on sale documents

Documents that describe or include products, methods, or services that are in public use or on sale also qualify as prior art. Depending on the restriction of the search, the document must include a date to prove that the product, method, or service is in public use or on sale before the effective date used in the search.

Use Cases

When do I need to conduct a patent validity search?

There are several reasons or use cases for conducting a patent validity or invalidity search. It can help a company make informed decisions regarding patent litigation, licensing and sale negotiations, and even market entry.

Use cases for a patent validity and invalidity search

1. Patent infringement and litigation

The primary reason for conducting an invalidity search is to challenge the validity of a patent. A party accused in a patent infringement case can use the search results to build a strong defense and challenge the patent in court or thru post-grant proceedings at the USPTO Patent Trial and Appeals Board (PTAB).

On the other hand, a validity search is conducted to assess a patent’s strength or identify potential weaknesses before engaging in litigation. This enables patent holders to anticipate and prepare for potential challenges that could be raised during legal proceedings.

2. ITC Section 337 Investigation

An ITC (International Trade Commission) Section 337 investigation is a legal proceeding conducted by the United States International Trade Commission under Section 337 of the Tariff Act of 1930. Section 337 prohibits unfair practices in import trade, such as intellectual property rights infringement or unfair competition by imported goods.

The purpose of a Section 337 investigation is to address unfair acts in the importation of products that harm domestic industries. These unfair acts can include patent, copyright, or trademark infringement, as well as trade secret misappropriation, false advertising, and other forms of unfair competition.While these investigations seek to address various forms of unfair competition, majority of complaints involve patent infringement.

If you are named as the respondent in a Section 337 investigation, there are various defenses at your disposal. A respondent in the case may prove non-infringement, cite exempted uses, or challenge the validity of the asserted patent

3. Licensing or sale negotiations

Before buying a patent, the acquiring party must assess the validity and enforceability of the patent in question. Licensing a patent without thoroughly evaluating its validity can expose the licensee to legal risks. If the patent is later found to be invalid or unenforceable, the licensee may face infringement claims, financial damages, and potential disruption to their operations.

A patent validity search helps identify any potential risks and allows the licensee to make informed decisions before entering into the licensing agreement.

4. Due diligence

Conducting a patent invalidity or validity search must be conducted during due diligence activities in mergers and acquisitions. By identifying any potential invalidity issues, the acquiring company can make informed decisions regarding the value of the target company.

5. Patent stress test

Stress-testing a patent in one’s portfolio is a common practice that allows the patent holder to assess the strength of a patent. By identifying weaknesses in a patent, a company may be able to avoid costly litigation and licensing fees.

1. Develop a search strategy

Prior art searching is not a straightforward task and requires a lot of tweaking before you get relevant results. Plan out a search strategy. Before starting an invalidity search, the subject matter must be understood by each individual involved in the search.

The scope of the search is very important. Properly identifying effective filing date of the patent in suit will set the parameters of your search.

2. Identify the inventive step

Looking at the patent file wrapper or prosecution history can help to identify which parts of the claim were deemed to be novel and inventive by the patent examiners. Determining the inventive concept allows you to prepare a good set of keywords for your search.

3. Optimize, optimize, optimize!

Taking notes of keywords and search strings that yield relevant and irrelevant results may help in trial and error.  You may also want to get all in-scope references by using very broad keywords and classifications but this may also result in a large number of references to review. Keywords that are too specific may result in high relevance but miss out on other references of interest. It is also important to identify synonyms of important keywords to be able to expand the search and capture as many relevant references as possible. Some databases allow the use of search operators such as boolean and proximity operators.

4. Utilize publicly available databases

It is also recommended to have a list of databases where searching for patents and NPLs is possible. USPTO, EPO, WIPO, and Google Patents are some patent databases where searching is possible. 

For NPLs, some of the databases are Google Scholar, ScienceDirect, and IEEE.  HighWire, BioMed Central, SciTech Connect, EBSCO, MEDLINEPlus Health Information, Computing Research Repository,,, etc. Some universities also make their students’ theses and dissertations available for public viewing or downloads.

5. Don't ignore the references cited on the patent itself

While patents may have numerous pages of cited references, there remains a possibility that both the applicant or inventor have properly reviewed all of them. Even if these references were submitted as part of patent application documents, it doesn’t mean that those submissions do not contain any disclosure, teaching, or suggestion that could invalidate one or more claims of the patent at issue.

More tips and tricks here.

6. A team of experts helps

While anyone can conduct a validity or invalidity search, it oftentimes becomes imperative to seek the help of a team of subject matter experts, researchers, and patent professionals.

Engaging patent research providers can become a cost-effective tool, especially when you have decided to go to court and challenge the patent-in-suit. A thorough, well-informed search can also help mitigate costs attributed to litigation, infringement, licensing. Parola Analytics offers patent attorney-led prior art searches and can be a useful resource for law firms and innovators alike. Find out more here.


Expert-led Patent Research

  • Extra layer of quality

    All our prior art searches are led and reviewed by U.S. registered patent attorneys. This ensures that there is both a legal and technical understanding of the subject matter.

  • Trusted by experts

    Over 5,000 patent searches performed for top law firms such as Fish & Richardson, Knobbe Martens, Quinn Emanuel, and many others.

  • Cost-effective, customizable solutions

    We are committed to finding the best solutions for and with our clients. Need a quick search? We provide a preliminary search option: a perfect springboard to jumpstart your search strategy.

Get in touch to find out more about our patent validity and other prior art search services.

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