Patent enforcement proceedings

Lawsuits and courts

What legal or administrative proceedings are available for enforcing patent rights against an infringer? Are there specialised courts in which a patent infringement lawsuit can or must be brought?

A patent owner can enforce its patent rights against an infringer in any federal district court that has personal jurisdiction over the defendant. A patent owner can also enforce its patent rights in an administrative proceeding before the US International Trade Commission (ITC). An action in the ITC is available only for potentially infringing goods being imported into the United States.

There are no specialised patent trial courts. However, appeals from both the ITC and federal district courts are heard exclusively by the Court of Appeals for the Federal Circuit. Appeals from the Federal Circuit are heard by the US Supreme Court.

Trial format and timing

What is the format of a patent infringement trial?

A patent trial begins with the plaintiff filing a complaint alleging infringement of one or more patents. The defendant (accused infringer) files an answer, alleging non-infringement and asserting various defences. The parties proceed to fact and expert discovery, motion practice, pretrial briefing and trial. If money damages are sought, the trial is before a jury. However, a case is tried by a judge when only equitable relief is available.

Parties introduce evidence primarily through live testimony, including both fact and expert witnesses. After providing their direct testimony, the witnesses can be cross-examined by the opposing counsel. Documents are included in evidence to the extent that they are admissible and relevant to the dispute. Affidavits are generally not accepted into evidence.

Expert witnesses are almost always involved in patent litigation cases, with each party typically retaining its own experts. In addition, a trial judge can appoint an expert to advise the court (this is typically done only for bench trials).

Patent infringement trials in district court typically take one to two weeks, although it can be longer for complex or multi-patent cases.

Proof requirements

What are the burdens of proof for establishing infringement, invalidity and unenforceability of a patent?

The patent holder must prove infringement by a ‘preponderance of the evidence’. This requires proof that it is more likely than not that the defendant either directly infringed a claim of the asserted patent, contributed to another’s infringement or induced another to infringe. The patent holder also has the burden of proving monetary damages and must do so by a preponderance of the evidence.

Patents are presumed to be valid. Thus, an alleged infringer must prove invalidity or unenforceability of a patent by ‘clear and convincing evidence’, which requires a finding that it is ‘highly probable’ that the patent is invalid or unenforceable. This is a more rigorous standard than the preponderance of the evidence standard, but not as rigorous as the ‘beyond a reasonable doubt’ standard that applies in criminal law.

Standing to sue

Who may sue for patent infringement? Under what conditions can an accused infringer bring a lawsuit to obtain a judicial ruling or declaration on the accusation?

A party suing for infringement must hold exclusive rights to the patent being asserted, such as a patentee or assignee. A licensee has standing to sue for patent infringement if it has received ‘all substantial rights’ in the asserted patent, such as an exclusive licensee. However, a non-exclusive licensee does not have standing to bring suit or to join a suit with the patentee because the licensee suffers no legal injury from infringement.

An accused infringer may file a declaratory judgment lawsuit if, based on the totality of the circumstances, there is a substantial controversy between the parties which is of sufficient immediacy and reality. This situation occurs typically when a patent holder sends a cease-and-desist letter or otherwise gives notice suggesting that the potential infringer may want to license the patent. Other categories of declaratory judgment actions include, for example: when a licensee disputes the validity of a licensed patent or that its products infringe the patent; and when a supplier files suit against a patentee who has threatened, or has sued, the supplier’s customers based on the supplier’s products or services.

Inducement, and contributory and multiple party infringement

To what extent can someone be liable for inducing or contributing to patent infringement? Can multiple parties be jointly liable for infringement if each practises only some of the elements of a patent claim, but together they practise all the elements?

Indirect infringement occurs when the defendant does not itself commit the infringing activity, but instead causes another party to do so. Someone can be liable for inducing infringement if they are aware of the asserted patent and have the specific intent to encourage another’s infringing activity. The plaintiff has the burden of showing that the alleged infringer’s actions knowingly induced the infringing acts to occur. The knowledge requirement can be met by showing either actual knowledge or wilful blindness (deliberate actions to avoid confirming a high probability of wrongdoing). In general, if the defendant reasonably believes that there is no infringement, then there is no liability for induced infringement.

A party is liable for contributory infringement by offering to sell or selling in the US, or importing into the US, a component or material for use in a patented process that constitutes a material part of the patented invention, with knowledge that the component is especially made or especially adapted for use in an infringing manner. Moreover, the item must not be a staple or article suitable for a substantial non-infringing use.

Multiple parties can be jointly liable for infringement if each of the parties practises only some of the claim limitations, but together the parties perform all of them as part of a joint enterprise. A single party can be liable for infringement by practising only some of the claim limitations, if it directs or controls another party that practises the remaining claim limitations.

Joinder of multiple defendants

Can multiple parties be joined as defendants in the same lawsuit? If so, what are the requirements? Must all of the defendants be accused of infringing all of the same patents?

Accused infringers may be joined as defendants in the same lawsuit if the allegations against the parties arise out of the same transaction relating to the making, using, importing into the US, offering for sale, or selling of the same accused product or process; and questions of fact common to all defendants will arise in the action. Thus, for example, if the parties have a commercial relationship to the accused products (eg, one of the parties sells a component and the other party uses the component), they could be joined in the same action.

Parties may not be joined as defendants in the same lawsuit based solely on allegations that they each have infringed the same patent-in-suit.

Infringement by foreign activities

To what extent can activities that take place outside the jurisdiction support a charge of patent infringement?

There are several circumstances under which activities taking place outside the US result in patent infringement. For example, an apparatus claim can be infringed if control of the system is exercised and its benefit is obtained in the US, even if components (for example, a server) of the claimed system are located outside of the US.

Foreign activities can also be used to establish patent infringement of method claims. If a product is imported into the US or sold, offered for sale or used within the US, and if a process used to manufacture the product satisfies the claim requirements, such activity can support a finding of infringement.

Another example is ‘export infringement’, which occurs if all or a substantial portion (quantitative, rather that qualitative) of the components of a claimed invention are made and assembled in the US, but the components are combined outside the country. To infringe, a party must either induce making the combination outside the US or the components must be supplied knowing that they were especially made for use in a claimed invention, intending that the components will be combined outside the US in an infringing manner. Export infringement is only applicable to apparatus claims; not method claims.

Infringement by equivalents

To what extent can ‘equivalents’ of the claimed subject matter be shown to infringe?

Infringement under the doctrine of equivalents occurs when the accused product or process is similar, but not identical, to the patented invention. It is an equitable doctrine developed by the courts to provide a mechanism to avoid patent infringement for insubstantial variations to the claimed invention.

There are two tests for determining equivalence, with both based on the state of the art at the time of infringement. Under the more commonly applied function-way-result test, an accused element is equivalent to a claim limitation when it performs substantially the same function in substantially the same way to achieve substantially the same result. Alternatively, the insubstantial differences test inquires whether the differences between the claim limitation and the element in the accused product or process are insubstantial.

There are a number of legal doctrines that limit the applicability of the doctrine of equivalents, including prosecution history estoppel, the all-elements rule, and the public dedication rule.

Prosecution history estoppel prevents a patentee from using the doctrine of equivalents to recapture subject matter that was surrendered to the patent examiner to obtain the patent.

The all-elements rule requires that the doctrine of equivalents be applied to the claims on an element-by-element basis, such that the accused product or process must contain each claim limitation or its equivalent. 

The public dedication rule prevents a patentee from relying on the doctrine of equivalents to capture subject matter that was publicly known at the time of invention. Thus, an accused infringer can practise the prior art and avoid infringement under the doctrine of equivalents. Similarly, the public dedication rule prevents recapture of subject matter that is disclosed in the patent specification but not claimed.

Discovery of evidence

What mechanisms are available for obtaining evidence from an opponent, from third parties or from outside the country for proving infringement, damages or invalidity?

Discovery of evidence in the US legal system is very broad, in that a party is entitled to information relevant to any claim or defence of any party in the lawsuit. This is achieved by requesting documents, seeking deposition testimony, asking written questions (interrogatories), and seeking to inspect the property of the opposing party and of non-parties. Typically, however, the range of documents that a non-party must produce is more limited than those that a party to the litigation is required to produce.

A number of courts have their own rules about discovery and case management practices that apply specifically to patent cases. For example, several courts require the parties to produce infringement or invalidity-related documents early in the case.

In addition, the identity of an expert witness who may provide testimony at trial must be disclosed during the discovery period, and the expert is required to provide the opposing party a written report that contains a complete statement of all opinions the expert will provide in the case and the basis and reasons for them.

An important limitation on discovery is attorney-client privilege, which can prevent the disclosure of confidential communications between a client and its attorney. Additionally, the work-product doctrine prevents the disclosure of an attorney’s thoughts and mental impressions prepared in anticipation of litigation.

Parties may take pre-trial discovery from non-parties outside the US if the party is in a country that is a signatory to the Hague Convention. Taking discovery under the Hague Convention is more cumbersome and time-consuming than doing so in the US. The requesting party must first ask the federal court in which the case is pending to issue a letter of request (also called a letter rogatory) to the appropriate authority in the foreign country that sets forth the discovery sought. The receiving authority will apply its own laws with respect to the discovery methods and procedures to be followed in obtaining the requested material.

Litigation timetable

What is the typical timetable for a patent infringement lawsuit in the trial and appellate courts?

The typical timetable for a patent infringement lawsuit varies depending upon the district court, and whether the case is governed by local patent rules designed to facilitate discovery and the case management schedule. The timetable is also affected by the number of other cases pending in the court; for instance, in 2019, the District of Delaware was the most active in the US for patent filings, accounting for 28 per cent of all cases.

In 2019, the median time for a patent case to conclude – measured from the filing of the complaint to a termination by any mechanism – was 199 days. However, the median increases to 661 days for cases that end in a summary judgment determination and is 780 days for cases that reach trial. More complex and multi-patent cases will typically take longer to resolve.

The timetable for the Federal Circuit to decide a case is typically about a year from the date the appeal is docketed.

Litigation costs

What is the typical range of costs of a patent infringement lawsuit before trial, during trial and for an appeal? Are contingency fees permitted?

According to the Report of the Economic Survey 2019 published by the American Intellectual Property Law Association, for an infringement case in district court involving a single patent where there is:

  • less than US$1 million at risk, the median cost through to the end of discovery is US$250,000 and the total median cost through trial and appeal is US$700,000;
  • between US$1 million and US$10 million at risk, the median cost through to the end of discovery is US$600,00 and the total median cost through trial and appeal is US$1.5 million;
  • between US$10 million and $25 million at risk, the median cost through to the end of discovery is US$1.23 million and the total median cost through trial and appeal is US$2.7 million; and
  • more than US$25 million at risk, the median cost through the end of discovery is US$2.38 million and the median cost through trial and appeal is US$4.0 million.


Cases involving multiple patents or cases involving very complex technology will tend to be more expensive. Contingency fees are permitted in patent litigation.


Court appeals

What avenues of appeal are available following an adverse decision in a patent infringement lawsuit? Is new evidence allowed at the appellate stage?

The Federal Circuit hears all appeals in patent cases. The US Supreme Court hears appeals from decisions of the Federal Circuit on a permissive basis, and only occasionally accepts patent cases for review.

An appeal is not a retrial or a new trial of the case, and thus new evidence is not allowed at the appellate stage. Instead, if the appellate court determines that an error occurred at the trial court then it may reverse the judgment and, if necessary, order a new trial to occur. Reversible errors are those that substantially affect the rights of the appealing party. Not all errors at the trial court are reversible. Some errors are deemed to be harmless such that they did not affect the case outcome.

Competition considerations

To what extent can enforcement of a patent expose the patent owner to liability for a competition violation, unfair competition, or a business-related tort?

Antitrust concerns are more likely to arise when parties enter licences. However, enforcement of a standard essential patent (SEP) can give rise to an antitrust claim if the patent owner agreed to license the SEP on fair, reasonable and non-discriminatory (FRAND) terms, but then attempts to obtain an injunction against an accused infringer. In addition, asserting a patent that was procured through fraud or other illicit conduct may constitute an antitrust violation.

Some states have passed laws that protect against infringement allegations made in bad faith by the patent owner. Such a scenario can arise when a patent owner sends a cease-and-desist letter or other notice. Facts that may show bad faith include threatening an infringement action without any intention of filing a lawsuit.

Alternative dispute resolution

To what extent are alternative dispute resolution techniques available to resolve patent disputes?

Arbitration and mediation are two types of alternative dispute resolution in patent disputes. In arbitration, a neutral arbitrator or panel of arbitrators will render a decision, which can be either binding or non-binding. In binding arbitration, the parties waive their right to a trial and agree that they will be bound by the arbitrator’s final decision; whereas in non-binding arbitration the final decision is not enforceable and either party can reject the decision and instead request a trial. Arbitration often involves a structured presentation of each party’s case by counsel through live witnesses, depositions, affidavits and documentary evidence.

Mediation is less formal than arbitration and involves a neutral mediator whose role is to help the parties settle their dispute. Typically, the parties provide written summaries of the dispute to the mediator in advance. The mediator often will alternately meet with each party in an effort to bring them together to a negotiated settlement. In contrast to arbitration, the mediator does not render a decision.

Because of the high costs involved in patent litigation, parties will sometimes proceed with alternative dispute resolution in parallel with litigation. In addition, many courts require the parties to engage in some form of ADR, usually mediation, prior to trial.

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The information in this chapter is accurate as of February 2020.