Before Filing a Patent Suit

Common situations.

• A patent owner sees a competitor's new product and wants to know what must happen before it can sue.
• A company receives a letter offering a license and wonders whether the letter lets it sue first.
• A business receives a demand and wants to know what to keep, whom to tell, and whether it needs a legal opinion.

For the patent owner.

Investigate before filing. Federal Rule of Civil Procedure 11 requires a reasonable inquiry before filing. In a patent case, that ordinarily means construing the asserted claims and comparing them with the accused product, usually by obtaining and examining it (View Eng'g, Inc. v. Robotic Vision Sys., Inc., 208 F.3d 981 (Fed. Cir. 2000); Q-Pharma, Inc. v. Andrew Jergens Co., 360 F.3d 1295 (Fed. Cir. 2004)). A thin investigation can lead to sanctions or a fee award (35 U.S.C. § 285).

Confirm ownership and standing. Check the assignment record, any licenses, and any co-owners before filing. A defect in standing can end the case. See Patent Basics for Litigation, with a Glossary.

Check the patent's health. Confirm that maintenance fees are paid, the patent has not expired, and no claims have been canceled in an earlier Patent Office proceeding. Review the file history for statements that narrow the claims.

Consider marking and notice. If the owner's or its licensees' products practice the patent and were not marked, damages run only from actual notice (§ 287(a)). A specific notice letter can start damages running, but it also has consequences:

• It can give the recipient grounds to file a declaratory judgment suit in a forum it prefers.
• Letters sent into a state can support personal jurisdiction over the patent owner there (Trimble Inc. v. PerDiemCo LLC, 997 F.3d 1147 (Fed. Cir. 2021)).
• Letters to end users in Texas must comply with the state's bad-faith demand letter statute (Tex. Bus. & Com. Code §§ 17.951-17.955).

Plan the forum. Venue in patent cases is limited (see Where Patent Cases Are Heard). The owner should also weigh whether to seek an exclusion order at the International Trade Commission.

Funding disclosures. Some courts require parties to disclose anyone with a financial interest in the outcome. In the Northern District of Texas, the certificate of interested persons must list all persons and entities financially interested in the outcome (N.D. Tex. L.R. 3.1(c), 3.2(e)). Check the local rules and the judge's standing orders before filing.

For the accused company.

Do not ignore the letter, and do not answer it in haste. A response can affect willfulness, jurisdiction, and later arguments about what the claims mean. See Responding to a Patent Infringement Claim and Receiving an IP Demand Letter.

Preserve documents. Once litigation is reasonably anticipated, relevant documents, source code, and electronic data must be preserved. A written litigation hold to the right custodians is standard practice.

Notify suppliers and insurers. Purchase agreements often contain indemnity clauses with notice deadlines. A buyer may also have a claim against a merchant seller under the Texas UCC warranty against infringement (Tex. Bus. & Com. Code § 2.312(c)). Most general liability policies exclude patent infringement, but some policies do cover it, so check every policy promptly.

Consider an opinion of counsel. A competent written opinion that the product does not infringe or that the patent is invalid can be evidence of good faith on willfulness. Failing to obtain one, or choosing not to present one at trial, cannot be used to prove willful infringement or intent to induce (35 U.S.C. § 298). Relying on an opinion waives privilege over its subject matter, so the decision is strategic.

Consider filing first. A company that faces a real and immediate controversy, judged under all the circumstances, may sue for a declaration of noninfringement or invalidity (MedImmune, Inc. v. Genentech, Inc., 549 U.S. 118 (2007)). A license offer that identifies the patent and the product can be enough (SanDisk Corp. v. STMicroelectronics, Inc., 480 F.3d 1372 (Fed. Cir. 2007)). Filing first lets the company pick the forum, within the venue and jurisdiction rules.

Consider the Patent Office. An inter partes review petition must be filed within one year after service of a complaint alleging infringement (§ 315(b)). Filing a declaratory judgment action challenging validity before petitioning bars the petition (§ 315(a)(1)); a counterclaim of invalidity does not. See PTAB Proceedings and Parallel Litigation.

Texas notes.

• Patent infringement claims belong only in federal court (28 U.S.C. § 1338(a)). Related state-law claims, such as breach of a license or a dispute over ownership, can be heard in Texas state courts, including the Texas Business Court when the case meets its thresholds. See Where IP Disputes Are Heard in Texas.
• The Texas Attorney General, not private parties, enforces the bad-faith demand letter statute.

Sources.

• Fed. R. Civ. P. 11.
• 35 U.S.C. §§ 285, 287(a), 298, 315(a)(1), 315(b).
• 28 U.S.C. § 1338(a).
• Tex. Bus. & Com. Code §§ 2.312(c), 17.951-17.955.
• N.D. Tex. L.R. 3.1(c), 3.2(e).
• View Eng'g, Inc. v. Robotic Vision Sys., Inc., 208 F.3d 981 (Fed. Cir. 2000).
• Q-Pharma, Inc. v. Andrew Jergens Co., 360 F.3d 1295 (Fed. Cir. 2004).
• Trimble Inc. v. PerDiemCo LLC, 997 F.3d 1147 (Fed. Cir. 2021).
• MedImmune, Inc. v. Genentech, Inc., 549 U.S. 118 (2007).
• SanDisk Corp. v. STMicroelectronics, Inc., 480 F.3d 1372 (Fed. Cir. 2007).

This guide is general information, not legal advice. Law checked through October 20, 2026. See the Disclaimer.