Patent discovery

Patent discovery is the federal civil discovery system overlaid by a contention-driven disclosure regime. The Patent Local Rules — pioneered in the Northern District of California and adopted in modified form across the major patent districts — require the patentee to commit to its theory of infringement early and require the accused infringer to commit to its invalidity theory shortly thereafter. Protective orders, prosecution bars, source code review, and ESI orders structure the rest of the case.

The rule

Discovery in patent cases proceeds under the Federal Rules of Civil Procedure, but it is heavily structured by Patent Local Rules that require the parties to disclose their substantive theories on a fixed schedule. Under those rules, the patentee serves infringement contentions early in the case identifying each accused product, each asserted claim, and a claim chart matching every claim element to a feature of the accused product. The accused infringer responds with invalidity contentions identifying each prior art reference, the basis for invalidity (anticipation, obviousness, written description, enablement, indefiniteness), and a claim chart for each reference.

This contention-and-claim-chart regime is a structural feature unique to patent litigation. It departs from notice pleading by forcing the parties to put substance on the table well before summary judgment, and it disciplines the rest of discovery — depositions, expert reports, and the Markman process — around a fixed factual frame.

Governing rules

Federal Rules of Civil Procedure

• Rule 26. Initial disclosures, scope and limits of discovery (proportionality), expert disclosures, work product and privilege, supplementation duty.
• Rule 30. Depositions on oral examination, including limits on number and duration and the deposition of corporations under Rule 30(b)(6).
• Rule 33. Interrogatories. Federal Rule limit of twenty-five per side is frequently expanded by court order in patent cases.
• Rule 34. Document requests and inspection of tangible things, including ESI.
• Rule 36. Requests for admission, often used to streamline authentication of patents and prior art.
• Rule 37. Sanctions for discovery violations.
• Rule 45. Subpoenas to non-parties.

Patent Local Rules — the contention regime

• P.R. 3-1 (Disclosure of Asserted Claims and Infringement Contentions). The patentee identifies each asserted claim, each accused instrumentality, and a chart locating each claim element in the accused product. The contention must also specify whether infringement is direct, indirect, or under the doctrine of equivalents, and whether it is literal or by equivalents.
• P.R. 3-2 (Document Production Accompanying Disclosure). The patentee produces conception and reduction to practice documents, prosecution history, ownership records, and any pre-suit licenses or settlement agreements.
• P.R. 3-3 (Invalidity Contentions). The accused infringer identifies each prior art reference, the basis for invalidity, and a chart for each reference. The contention covers § 102, § 103, and where applicable § 112 invalidity grounds.
• P.R. 3-4 (Document Production Accompanying Invalidity Contentions). The accused infringer produces the source code, technical documentation, and prior art that supports its noninfringement and invalidity positions.

The Eastern District of Texas, Northern District of California, and District of Delaware use materially similar versions of these rules. The Western District of Texas's standing order varies in timing and form but tracks the same substantive logic.

The framework: contentions, document production, depositions

Initial disclosures and Rule 26(f)

Within a few weeks of the complaint, the parties confer under Rule 26(f) and exchange initial disclosures under Rule 26(a)(1). The Rule 26(f) report typically proposes the case schedule, including dates for the contention exchange under the Patent Local Rules.

Infringement contentions

P.R. 3-1 contentions are typically due fourteen days after the initial case management conference. The chart must show each claim element in the accused product. Courts have repeatedly held that contentions cannot consist of "string cites" or boilerplate; they must put the accused infringer on adequate notice. O2 Micro Int'l Ltd. v. Monolithic Power Sys., Inc., 467 F.3d 1355 (Fed. Cir. 2006).

Invalidity contentions

P.R. 3-3 contentions follow forty-five days later. The contentions must identify each item of prior art, including the date and country of each reference, a chart showing each element disclosed by the reference, and any motivation to combine for obviousness theories. O2 Micro applies to invalidity contentions as well.

Amendment standard

Once contentions are served, they may be amended only on a showing of good cause. O2 Micro, 467 F.3d at 1366. Good cause turns on the diligence of the party seeking amendment, the importance of the new information, the prejudice to the opposing party, and the availability of a continuance. Late amendments to add new accused products or new prior art are routinely refused.

Document production

Document production proceeds under Rule 34. Patentees produce ownership and licensing records, prosecution histories, and conception and reduction-to-practice documents. Accused infringers produce technical documentation, financial records relevant to damages, and documents reflecting design and development. ESI orders (discussed below) govern format, custodian selection, search, and production protocols.

Source code review

Source code is typically produced for inspection on a stand-alone, non-networked computer at a designated secure facility — usually counsel's office. The protective order limits the number of pages that may be printed, restricts access to outside counsel and designated experts, and prohibits any copying or removal. Courts disfavor over-restriction but routinely enforce reasonable limits to protect trade secrets.

Depositions

Patent cases typically expand the Rule 30 default of ten depositions. Common deposition targets include the named inventors, the prosecuting attorney (subject to limits on prosecution privilege), Rule 30(b)(6) corporate witnesses on technical operation and on financials, third-party prior art witnesses under Rule 45, and damages witnesses including licensing personnel.

Interrogatories and contention interrogatories

Contention interrogatories are heavily used in patent cases — for example, "State the basis for each contention that the accused product practices each element of the asserted claims." The Patent Local Rules' contention regime does not displace contention interrogatories; rather, the two operate in parallel.

Expert discovery

Expert reports under Rule 26(a)(2) follow the close of fact discovery and the claim construction order. Most schedules separate opening reports (each side serves on issues for which it has the burden), responsive reports, and reply reports.

Burden, timing, and key deadlines

The party seeking discovery generally bears the burden of justifying the request when proportionality is contested. Rule 26(b)(1) limits discovery to nonprivileged matter relevant to a claim or defense and proportional to the needs of the case.

Typical patent case milestones, measured from the initial scheduling conference:

• Day 0: Initial case management conference. Schedule entered.
• Day 14: P.R. 3-1 infringement contentions and P.R. 3-2 document production from patentee.
• Day 60: P.R. 3-3 invalidity contentions and P.R. 3-4 document production from accused infringer.
• Months 3–7: Document production, source code review, fact depositions.
• Months 6–9: Markman process. See Markman hearings.
• Months 9–12: Continued fact discovery, narrowing of asserted claims and prior art.
• Months 12–14: Close of fact discovery; opening expert reports.
• Months 14–16: Responsive expert reports; expert depositions.
• Months 16–18: Summary judgment and Daubert motions.
• Months 18–24: Pretrial conference and trial.

Interaction with related procedural mechanisms

Protective orders and the prosecution bar

Patent cases rely on stipulated or court-ordered protective orders that designate documents as Confidential, Highly Confidential — Outside Counsel Only, and Source Code. The Federal Circuit addressed prosecution bars in In re Deutsche Bank Trust Co. Americas, 605 F.3d 1373 (Fed. Cir. 2010), holding that whether a litigation attorney may be barred from patent prosecution involving the same technology is decided by balancing the risk of inadvertent disclosure against the harm of denying counsel of choice. The court instructed district courts to make case-specific determinations rather than impose a uniform rule, and to consider the attorney's role in prosecution, the proximity of the technology, and the duration of the bar.

ESI orders

Most districts use a standing or model ESI order. The order typically limits email discovery to specified custodians and search terms, addresses metadata, defines production format (TIFF with load files, native files for spreadsheets), and resolves cost-shifting for difficult productions. The Federal Circuit endorsed targeted email discovery in In re Bear Creek Technologies, Inc., 504 F. App'x 879 (Fed. Cir. 2013), reinforcing the trend toward proportionality.

Privilege

Patent cases involve unique privilege issues: communications with prosecution counsel may be claimed as attorney-client communications, but communications with patent agents are governed by the Federal Circuit's recognition of a separate patent-agent privilege in In re Queen's University at Kingston, 820 F.3d 1287 (Fed. Cir. 2016). Common interest privileges and joint defense agreements are also routine.

PTAB estoppel

Where the accused infringer has filed an IPR, the petitioner is estopped under 35 U.S.C. § 315(e)(2) from raising in district court any prior art ground it raised or reasonably could have raised in the IPR after a final written decision. See IPR estoppel. The estoppel reshapes invalidity contentions and forces the petitioner to plan IPR and district-court invalidity strategy together.

Standing

Discovery into standing may begin early where ownership is in dispute, especially in cases involving complex assignment chains or licensing transactions.

Discovery in ITC investigations

Discovery in ITC Section 337 investigations is far more compressed and aggressive than in district court, with deposition limits often raised to thirty per side and discovery on a roughly five-month track.

Practical notes

Take contentions seriously

Contentions are not pleadings. They are evidence-grade commitments that drive expert reports and trial. Boilerplate contentions invite motions to strike and amendments later in the case become difficult.

Plan source code review

Source code review is slow, expensive, and disorienting. The accused infringer should produce a complete and well-indexed code repository; the patentee should send a competent reviewer with a focused checklist. Print quotas and timing windows must be negotiated up front.

Stipulate ESI early

An ESI dispute that surfaces six months into the case is a costly distraction. Stipulate, before discovery starts, on custodians, search terms, format, and metadata fields.

Protect the prosecution bar

Where the protective order includes a prosecution bar, ensure clear procedures for ethical screens, lateral attorney movements, and the duration of the bar. The ambiguity rate at the end of cases is high.

Mind the supplementation duty

Rule 26(e) requires supplementation of disclosures and discovery responses. In patent cases this duty is acute for new accused products, new prior art, and new licensing information that could affect damages.

Use third-party subpoenas strategically

Many critical witnesses — prior art authors, former employees, foundries, customers — are not parties. Rule 45 subpoenas should be timed to integrate with the deposition schedule and to allow for objections, motion practice, and potential transfer of subpoena disputes to the issuing court.

Pressure points

Proportionality and the cost of patent discovery

The 2015 amendments to Rule 26(b) elevated proportionality. Courts increasingly limit broad email and ESI discovery and require focused custodian and search-term lists. The line between targeted discovery and inadequate discovery remains contested.

Foreign discovery

Many patent cases involve foreign defendants, foreign witnesses, and foreign prior art. Discovery from foreign affiliates raises Hague Convention questions and, in some jurisdictions, blocking statutes. The Federal Circuit has addressed personal jurisdiction over foreign affiliates but has left much of the discovery mechanics to the district courts.

Prosecution bar scope

Whether a prosecution bar reaches PTAB proceedings remains contested. Some courts have extended bars to IPR participation; others have held that IPR work, because it lacks the claim-amendment hazard of original prosecution, falls outside the Deutsche Bank rationale.

Source code remote review

Remote source code review — once exotic — became routine during 2020 and remains contested. Producing parties prefer in-person review for security reasons; reviewing parties press for remote access on cost grounds.

AI-assisted review

The use of technology-assisted review (TAR) and now machine-learning-aided review for ESI is widely accepted but raises disclosure questions: must a producing party disclose its TAR protocol, training set, and confidence thresholds?

See also

• Markman hearingsThe claim construction process that contentions feed into.
• Standing in patent casesDiscovery into ownership, assignments, and licensing.
• Patent venueLocal patent rules vary by venue and shape discovery sequencing.
• Literal infringementThe substantive standard for which infringement contentions are written.
• AnticipationThe substantive standard for § 102 invalidity contentions.
• ObviousnessThe substantive standard for § 103 invalidity contentions.
• Written description and enablementSection 112 invalidity grounds that must be charted.
• Inequitable conductA defense whose pleading and discovery raise particularity issues.
• Inter partes reviewParallel PTAB proceedings often shape district court discovery scope.
• IPR estoppelEstoppel that shapes invalidity contentions.
• E.D. Tex.The original Patent Local Rules and contention regime.
• N.D. Cal.The patent local rules that pioneered the contention model.
• D. Del.Delaware default standards for discovery and ESI.

Authorities

Statutes and rules

• Fed. R. Civ. P. 26 (general provisions and proportionality)
• Fed. R. Civ. P. 30 (depositions)
• Fed. R. Civ. P. 33 (interrogatories)
• Fed. R. Civ. P. 34 (document production and ESI)
• Fed. R. Civ. P. 37 (discovery sanctions)
• Fed. R. Civ. P. 45 (subpoenas)
• 35 U.S.C. § 315(e)(2) (IPR estoppel)
• E.D. Tex. Patent Local Rules 3-1 to 3-4
• N.D. Cal. Patent Local Rules 3-1 to 3-4
• D. Del. Default Standard for Discovery
• W.D. Tex. Order Governing Proceedings — Patent Cases

Cases

• In re Deutsche Bank Trust Co. Americas, 605 F.3d 1373 (Fed. Cir. 2010)
• O2 Micro Int'l Ltd. v. Monolithic Power Systems, Inc., 467 F.3d 1355 (Fed. Cir. 2006)
• In re Queen's University at Kingston, 820 F.3d 1287 (Fed. Cir. 2016)
• In re Bear Creek Technologies, Inc., 504 F. App'x 879 (Fed. Cir. 2013)

Last reviewed: 2026