IP Law Essentials

Navigating Fact Discovery in a Patent Case


In nearly any litigation, facts are disputed and must be established by the party with the burden of proof. How do you meet that burden in a patent case? The answer depends on whether you are the patent owner seeking redress, or a defendant caught off-guard by a competitor's claims. Below, we discuss common tools that parties use to obtain documentary, testimonial, and written evidence during discovery in a patent case. These tools include requests for production or inspection, interrogatories, requests for admission, depositions, and subpoenas. Though it can be tedious, discovery is critical to a case. How a party responds during discovery greatly influences what evidence and arguments that party can use later in a case, including at trial or in a motion asking the court to decide an issue without having to go to trial (e.g., a motion for summary judgment).

What is the scope of discovery?

The scope of discovery in the United States is broad as compared to other countries, and governed by Federal Rule of Civil Procedure ("Federal Rule") 26. This rule states:

Unless otherwise limited by court order, the scope of discovery is as follows: Parties may obtain discovery regarding any nonprivileged matter that is relevant to any party's claim or defense and proportional to the needs of the case, considering the importance of the issues at stake in the action, the amount in controversy, the parties' relative access to relevant information, the parties' resources, the importance of the discovery in resolving the issues, and whether the burden or expense of the proposed discovery outweighs its likely benefit. Information within this scope of discovery need not be admissible in evidence to be discoverable.

Fed. R. Civ. P. 26(b)(1). Put simply, a party can ask for any evidence that is relevant to a case, provided that such requests are not disproportionate to the needs of that case.

What are the tools for document discovery?

The two main tools for document discovery are requests for production ("RFP") and requests for inspection.

  1. Requests for Production (RFPs) or Document Requests

RFPs are written request for documents, electronically stored information ("ESI"), and tangible objects. Although Federal Rule 34 allows an unlimited number of RFPs, many parties and courts may seek to limit this number by stipulation or by local rules and standing orders of a court. The party receiving a document request must respond in writing within 30 days by stating its objections to the request and whether it will produce any of the requested documents. Often the requested documents are provided on a rolling basis starting with the objections as the responding party continues to gather and process documents within the scope of the requests.

In patent infringement lawsuits, patent holders and patent defendants use document requests to obtain relevant evidence. For example, the patent holder may request documents related to the design and development of the accused product, as well as documents related to sales and marketing of those products. Similarly, a patent defendant may request from the patent holder documents related to conception and reduction to practice of the alleged invention and the patentee's efforts to commercialize it. It is rare to see a case where the parties agree on the scope of what is "relevant," and parties typically negotiate these differences throughout discovery, with the most critical issues presented to the court, if necessary.

Documents responsive to document requests may be stored throughout a company, including on shared servers, individual employee computers, corporate document repositories, and databases. Because of the voluminous nature of documents stored electronically, parties frequently enter into an ESI agreement that specifically addresses how electronic documents, including email, will be searched, collected, and produced. Look on Fish’s Intellectual Property Law Essentials next month for discussion of ESI agreements.

  1. Requests for Inspection

Although less common than requests for documents, Federal Rule 34 also allows one party to request to inspect documents or things in possession of another party. For example, in a patent case, a patent holder may request to inspect the manufacturing process used to produce the accused product. Similarly, a patent defendant may request to inspect one-of-a-kind or rare physical prior art. In some instances, a party will respond to a document request by making the requested subject matter available for inspection thereby allowing the responding party to exert greater control over the dissemination of information. This is often the case when dealing with requests to review source code relating to products accused of infringing a patent.

How is testimonial evidence collected?

The primary tool for testimonial evidence is through the taking of a deposition, which is typically conducted via live questions and answers between a witness and a lawyer in the presence of a court reporter. Though less frequently used, depositions may also be taken by written questions, where a witness answers written questions in the presence of a court reporter. Importantly, witnesses from either party and even non-parties, via subpoenas, can be deposed.

Federal Rule 30 allows for 10 depositions to be taken by a party without leave of court. The rules also limit depositions to 7 hours of testimony on the record in a single day. Oftentimes, parties will propose their own limits with respect to depositions at the outset of a case. A party may request to take the deposition of specific employees of an opposing party - referred to as an individual deposition or a 30(b)(1) deposition, or it may ask the opposing party to supply a witness prepared to testify about the party's knowledge of specified subjects - referred to as a corporate deposition or a 30(b)(6) deposition.

The plaintiff in a patent case typically seeks to depose individuals from the defendant who are knowledgeable about the design and development of the accused product and how it works, the importance of the accused features of the product, and the sales and profits of the accused product. The defendant often takes the deposition of the named inventors, individuals with knowledge of the company's licensing or practicing of a patent, and third party witnesses knowledgeable about prior art information.

How is written evidence collected?

Written evidence is typically collected in the form of questions and answers called interrogatories and requests for admission.

  1. Interrogatories

Interrogatories are written questions served on a party, which ask for written answers. It is one of the more powerful discovery tools available to the parties. Federal Rule 33 allows 25 interrogatories per side by default, but the parties can request the court to modify this limit. The party receiving an interrogatory must respond within 30 days, by providing written responses, by identifying documents that contain the answers, and/or by objecting to the interrogatory. Importantly, even after an answer is served, the answering party has a duty to supplement its response when it learns new information that impact its answer.

For example, the patentee may request the defendant to: (1) provide information about when and how the defendant first became aware of the asserted patent; (2) provide information related to any non-infringing alternatives; and (3) provide explanation of how it intends consumers to use the accused functionality. Defendants commonly use interrogatories to force the patent holder to: (1) identify any of the patentee's products sold that practice the asserted patent; (2) explain how the patent was conceived and reduced to practice, along with identifying documents that support that narrative; (3) identify knowledge of the prior art; and (4) identify any evidence of secondary considerations supporting the non-obviousness (or novelty) of the claimed invention.

Depending on the court and whether local rules require the parties to separately serve infringement and invalidity contentions, interrogatories may also be used to seek a party's position as to why an accused product infringes a patent, or why a patent claim is invalid.

As alluded to earlier, what a party does or does not disclose in response to these interrogatories heavily impacts what that party may argue once fact discovery has closed. For example, if a party seeks to argue that an accused component of a product satisfies a particular element of a patent claim, and could have but failed to identify this theory in response to an interrogatory asking for this information, a court is likely to prohibit the party from later making that argument.

  1. Requests for Admission (RFAs)

RFAs are written statements that one party submits to another party, asking it to admit that each statement is true. Federal Rule 36 allows an unlimited number of RFAs. The responding party must admit or deny the truth of each statement, or state that it lacks sufficient evidence or knowledge to admit or deny the statement. An RFA is deemed admitted unless answered. Also, the receiving party may not simply cite lack of knowledge or information as their reason for failing to admit or deny the requested information. It must make a good faith effort to answer.

RFAs are commonly used to isolate truly undisputed facts that need not be proved at trial, thus helping to streamline the case. For example, they can be used to show when particular prior art was publicly available, claim limitations that the parties agree are present in an allegedly infringing product or prior art reference, or most commonly, that particular documents are authentic.

How do you get discovery from non-parties?

A subpoena is the tool that permits a party to request a non-party, also called a third party, to provide information in a litigation. Subpoenas are allowed by Federal Rule 45. Typically, subpoenas are used to obtain documents or witness testimony from a non-party on a narrow issue in the case. A non-party served with a subpoena must respond to it, but can request relief from the court if the requests are unduly burdensome.

Both patent holders and defendants can use subpoenas to develop evidence in a patent lawsuit. For example, a patent holder may issue a subpoena to an inventor of the asserted patent who is not employed by the patent owner to obtain information related to the alleged invention, or a patent defendant may issue a subpoena to a third party to obtain information related to a prior art system that was developed by the third party.


For a discussion of what discovery is available during inter partes review ("IPR") before the Patent Trial and Appeal Board ("PTAB"), as opposed to during patent litigation, read What Discovery is Available during Inter Partes Review.

More questions? Contact the authors or visitFish's Intellectual Property Law Essentials.