In the United States, the initiation process for patent infringement cases is as follows: A patent infringement lawsuit officially begins when an individual or organization holding patent rights (the plaintiff) files a legal document called a "complaint" with a federal district court. This complaint details the parties involved—the plaintiff and the defendant—as well as the specifics of the allegedly infringed patent. Typically, the complaint provides a detailed description of the defendant's alleged infringing activities, such as manufacturing or selling a specific product. Additionally, the complaint outlines the different types of legal remedies the plaintiff seeks from the court. Importantly, at the time of filing, the complaint does not need to contain specific evidence proving the defendant's infringement; it only needs to state the plaintiff's legal claims and the underlying facts. After filing the complaint, the plaintiff is required to deliver (or "serve") a copy to the defendant.

In U.S. patent litigation, defendants typically have 21 days to respond after the plaintiff's complaint is served, though this deadline can often be extended by agreement. There are two main forms of response from the defendant: filing an answer or a motion to dismiss. In the answer, the defendant must respond to each factual allegation in the plaintiff's complaint, typically by admitting or denying each one. In litigation, any allegation not denied is considered admitted. The defendant must also raise all affirmative defenses, such as claiming the patent is invalid, and bear the burden of proof for these defenses. Like the complaint, the purpose of the answer is to inform about the nature of the defenses, not to provide detailed evidence supporting them. Additionally, the defendant can include counterclaims against the plaintiff in their answer, effectively suing the plaintiff and becoming a "counterclaim plaintiff." The plaintiff then has 21 days to respond to the defendant’s counterclaims. In patent cases, defendants often counterclaim that they did not infringe the plaintiff's patent or that the patent is invalid.

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On the other hand, the defendant can also file a motion to dismiss at the start of the litigation, asking the court to dismiss the plaintiff’s lawsuit without considering evidence supporting the plaintiff’s claims. This motion is usually based on several reasons, like the court lacking jurisdiction over the defendant, the plaintiff not being the true patent holder, the complaint lacking a credible basis for infringement claims, or the patent being apparently invalid. If the defendant files a motion to dismiss within the answer period (including any extensions), they do not need to submit an answer until the court decides on the motion. If the motion to dismiss is denied, the defendant still has 14 days to file an answer.

In patent litigation cases, the defendant may concurrently initiate a procedure at the United States Patent and Trademark Office (USPTO) to challenge the validity of the patent involved in the case. These procedures are commonly referred to as "post-grant" procedures because they are initiated at the USPTO after the patent has already been granted. The most common of these procedures is Inter-Partes Review (IPR), where the defendant can challenge the validity of the patent based on prior patents or printed publications that predate the patent application. The defendant can file for IPR within one year of receiving the patent infringement complaint or proactively before initiating any legal action. A successful IPR may result in one or more patent claims being declared invalid. After completing an IPR, the defendant is precluded from contesting in court any invalidity defenses that were or could have been raised during the IPR, a principle known as "estoppel."

After filing for IPR, defendants often request the district court to stay the related patent litigation until the USPTO's parallel procedure concludes. Under regulations, except in special circumstances, IPR is usually required to be concluded within 18 months of the challenging party's filing. Since the outcome of the IPR can significantly simplify the case, many judges agree to stay the litigation. If the IPR renders all patent claims involved in the litigation invalid, it effectively leads to the termination of the litigation in federal court.

Additionally, there are other types of post-grant procedures that can be initiated at the USPTO, though they are less frequently used in litigation, such as Post-Grant Review, Ex-Parte Reexamination, Supplemental Examination, and Derivation Proceedings. Post-Grant Review, for example, is a procedure for challenging newly granted patents within the first nine months post-grant. It allows for questioning multiple aspects of a patent, including its novelty and non-obviousness, based on any grounds of invalidity, including but not limited to prior patents or printed publications.

Once the defendant receives the plaintiff's complaint, the presiding judge organizes a meeting with the attorneys of both parties called a "Case Management Conference," sometimes also known as an Initial Pretrial Conference or Scheduling Conference. The primary purpose of this meeting is to establish a framework for controlling the litigation process. Before the meeting, the plaintiff’s and defendant’s attorneys are required to negotiate face-to-face to reduce the number of issues that might need the judge's ruling within the established framework. During the conference, various issues are discussed and decided, such as setting a timeline for the case, determining durations for evidence disclosure and deadlines for specific disclosures, and establishing specific trial dates or date ranges based on the judge’s and court’s decisions. Due to the complexity of cases and varying court schedules, the time for a case to go to trial can range from one year to three years.

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Moreover, the Case Management Conference also addresses issues related to limitations on discovery. Discovery is a process that allows the litigation parties to investigate the facts of the case, including demanding copies of documents, answering written interrogatories, and providing sworn testimonies from the opposing party. Although court rules limit the amount of permissible discovery, parties often request the court to modify or supplement these limits.

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Particularly, limitations on discovery, such as the number or duration of witness testimonies, are often a point of contention between parties. Additionally, the disclosure of Electronically Stored Information (ESI), such as emails, electronic documents, and databases, is a significant topic in the Case Management Conference. Given the extensive storage of electronic information by modern companies, parties usually need to agree on the types of ESI to be disclosed and methods of search, such as limiting searches to specific employees' files or using keywords.

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In addition to the above, courts in patent cases often issue protective orders, restricting access to certain information and prohibiting the disclosure of confidential information that must be revealed to opposing lawyers during discovery. The details of such protective orders are usually negotiated by the parties before the Case Management Conference, and if there are disagreements, they are resolved by the judge. Common disputes during protective order negotiations include issues of access, handling the sensitivity of source code, and implementing “patent prosecution bars.” Patent prosecution bars prevent individuals who access confidential information from filing patent applications on the same subject matter at the USPTO.

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Furthermore, the parties may negotiate the scope of disputes involved in the case, such as limiting the number of patent claims or the proportion of prior art, to simplify case handling. Finally, many judges explore the possibility of mediating disputes between parties at the Case Management Conference and arrange mediation deadlines as appropriate.

Following the Case Management Conference in U.S. patent litigation, the parties enter the fact discovery phase, a critical part of the litigation process where parties gather evidence and information related to the case from each other or third parties. This stage enables each party to collect evidence supporting their position and to understand the evidence and arguments of the opposing side. The duration of the fact discovery phase varies depending on the complexity of the case and the court's schedule, ranging from six months to several years. Typically, parties can engage in discovery regarding any matters related to any claims or defenses of the case that are not protected by attorney-client privilege or work product privilege.

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During the discovery process, the litigation parties have various methods for obtaining evidence, including document requests, interrogatories, and requests for admissions. Document requests involve written demands to the opposing party for documents, Electronically Stored Information (ESI), tangible items, or inspections of a location. The party receiving the request must respond in writing within 30 days, deciding whether to provide the requested information. Interrogatories are written questions posed to the opposing party, requiring written responses, typically within 30 days of receipt. Requests for admissions ask the opposing party to confirm the truth of certain factual statements, which helps to simplify undisputed facts during trial.

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Parties can also obtain evidence from third parties by issuing subpoenas for documents or depositions. Depositions are out-of-court proceedings where a witness answers lawyers' questions under oath, and the testimony can be used later in court. Furthermore, infringement and invalidity contentions are also part of fact discovery. In some courts, parties are required to exchange detailed contention charts where the plaintiff explains how the defendant allegedly infringes the litigated patent, and the defendant provides reasons why they believe the patent is invalid. This exchange of contentions typically occurs early in the discovery phase, further narrowing the scope of evidence related to these contentions.

In patent-related legal disputes, which often involve complex technical and legal issues, expert witnesses play a crucial role. These experts, hired separately by each disputing party, are primarily responsible for explaining technical details of the case to the jury, interpreting relevant legal issues, and providing professional opinions. Their testimonies are often central to the case, as ideal expert witnesses not only deeply understand the dispute’s intricacies but can also effectively convey their perspectives to the jury.

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Before testifying in court, expert witnesses must provide one or more written reports to the opposing attorneys. These reports outline the main points they plan to discuss during the trial. In addition, expert witnesses usually participate in pre-trial depositions, a process for questioning and clarifying their reports. During this stage, opposing attorneys interrogate the content of the reports, seeking evidence advantageous for cross-examination in court. This process, known as "expert discovery," offers both parties the opportunity to understand the evidence and opinions the opposing experts will present.

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In patent trials, two types of experts are generally employed: technical experts and damages experts. Technical experts provide analyses and opinions on patent infringement or validity, while damages experts focus on assessing the patent’s economic value and the financial impact of infringement. The process of selecting and hiring experts should begin several months or even a year in advance. The selection of experts is a complex interactive process, involving the verification of candidates' qualifications, interviews, and assessments of their strengths and weaknesses. Experts are typically sourced through three avenues: client recommendations, attorneys' personal experiences, or professional organizations.

In patent law, the numbered sentences at the end of a patent document, known as "claims," define the legal boundaries of the patent's protection. The precise articulation of these claims is crucial for determining the validity of a patent and the existence of infringement. In patent cases, parties often disagree on the meaning of key terms in the claims, necessitating a pre-trial ruling by a judge. This process, commonly referred to as "claim construction," significantly influences the final verdict of the case and can sometimes even determine all related legal liabilities.

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In 1996, the U.S. Supreme Court, in the case of Markman v. Westview Instruments, Inc., ruled that the legal interpretation of patent claims should be determined by the trial judge, not the jury. This decision led to the near-universal requirement of a pre-trial hearing in patent cases, often known as a "Markman hearing." During this hearing, the parties ask the judge to define or "construe" specific terms within the patent claims. Typically, judges issue their claim construction rulings before the end of the fact discovery process or sometimes after the trial has begun. In the construction process, judges generally rely on the overall context of the patent document and a detailed analysis of the patent specification, along with a review of the patent's prosecution history, to ascertain the original meaning of the terms in the claims.

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The specific timing and procedure for claim construction vary among district courts and judges. Generally, the construction process begins with the parties identifying the claim terms they believe require judicial interpretation and attempting to reach an agreement on their proper construction. Terms on which consensus cannot be reached are then submitted to the court for determination. Several months before the Markman hearing, parties engage in a summary judgment phase, which is the preliminary stage of the claim construction process. During this period, both sides prepare relevant evidence and arguments to present to the judge at the hearing.

In patent litigation, the primary role of a jury is to resolve disputed factual issues to determine which party should prevail in the dispute. However, in certain situations, a party may believe there are no material factual disputes that require a jury's resolution, leading them to file a motion for summary judgment. This motion seeks a court ruling based directly on the existing facts without substantial factual disputes. For example, a defendant might argue that, based on undisputed facts, their product’s operation clearly does not fall within any of the claimed patent rights alleged to be infringed. Such motions can resolve either the entire case or specific ancillary issues, such as whether certain documents should be considered prior art or whether certain invalidity defenses should go to the jury.

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Most summary judgment motions are filed after the completion of fact and expert discovery, the end of claim construction, and before the start of the trial. At this stage, parties and the court explore ways to simplify issues and expedite the trial. Judges typically set deadlines for filing summary judgment motions and sometimes schedule hearings for oral arguments to supplement written submissions. In some instances, judges may permit early filing of motions, such as before addressing procedural motions. This strategic choice can offer tactical advantages, particularly in common types of summary judgment motions like infringement/non-infringement, validity/invalidity, and damages issues. For instance, regarding infringement, a defendant might argue that the plaintiff cannot prove infringement based on undisputed facts. On validity issues, either party might claim certain patent claims are invalid based on legal issues or the results of claim construction. In terms of damages, summary judgment motions might be used to challenge unsupported damages claims, such as lost profits or enhanced damages based on willful infringement.

As the trial phase of a patent litigation approaches, usually one to two months before the court date, parties enter an intensive trial preparation phase. This stage encompasses various activities, including finalizing witnesses, preparing trial exhibits, and organizing logistics for the trial venue. During this period, parties often submit a series of pre-trial motions aimed at requesting the judge to resolve various issues related to the conduct of the trial. These motions can include requests to exclude unreliable expert testimony, petitions to bifurcate the trial into different phases for separate issues, and motions for pre-trial rulings on the admissibility of evidence or attorney conduct, often referred to as "motions in limine" to prevent prejudice.

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In the trial preparation phase, litigation teams engage in extensive preparatory work. This involves outlining witness testimonies and developing cross-examination strategies, identifying evidence to be presented during trial, creating charts and presentation materials, training witnesses for effective testimony delivery, and conducting mock trials and focus groups to gauge potential jury reactions. Additionally, preparation includes drafting opening statements and closing arguments, as well as arranging for depositions of witnesses who cannot appear in court. As the trial date nears, the court issues pre-trial orders, setting out the basic rules for the trial, such as the order of presenting evidence, scheduling of witness appearances, and time allocations for attorneys from both sides. In the pre-trial conference, parties negotiate and argue over these rules and preliminary jury instructions to ensure a smooth conduct of the trial.

In patent litigation cases, jury trials are common, especially when disputes involve monetary damage compensation. Such trials typically last one to two weeks and are adjudicated by a jury of 6 to 8 local citizens. Due to the jury members' general lack of specialized knowledge in patent technology, substantial time during the trial is often devoted to educating them about relevant technologies, the patented invention, the accused infringing product or process, and any prior art that may render the patent invalid. In this context, clearly and understandably communicating the technical dispute to the jury becomes crucial for the success of the case.

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The jury selection process includes a voir dire phase, where prospective jurors answer questions from the judge or attorneys. Based on these responses, the parties may request to exclude certain jurors. Parties can exclude jurors either peremptorily (without needing to provide a reason) or for cause (e.g., bias or pre-existing knowledge about the case), although the number of peremptory exclusions is limited. Once the jury is selected and preliminary instructions are given, the trial begins with opening statements. This is the chance for each side to present its version of the case to the jury for the first time, though arguing evidence is not allowed at this stage.

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Following the opening statements, both parties typically present evidence in the same order (plaintiff first, followed by defendant), including witness testimonies and physical evidence. The plaintiff presents evidence first to establish infringement of their patent, followed by the defendant’s rebuttal and possibly evidence of the patent's invalidity. After the evidence presentation, attorneys from both sides have the opportunity to make closing arguments, attempting to persuade the jury. The judge then provides jury instructions, clarifying the legal principles they must follow in deliberations. The jury's verdict often involves decisions on patent infringement and validity. Post-trial, the losing party may file post-trial motions, requesting the judge to overturn the jury's verdict due to insufficient evidence or errors during the trial. If the verdict favors the plaintiff, they may also request the court to issue injunctions, order patent royalties, or increase the damages awarded.

After a district court renders its judgment and addresses all post-trial motions, the losing party has the right to file a notice of appeal. This notice is typically required within 30 days of the district court's final judgment, or within 30 days of the court’s ruling on any motions to alter or amend the judgment, whichever date is later. The appeal is then directed to the Federal Circuit Court of Appeals, which specializes in patent cases.

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Contrary to other civil litigation cases typically reviewed in one of the twelve regional circuit courts of appeals in the United States, all appeals involving patent law are handled by the United States Court of Appeals for the Federal Circuit, located in Washington D.C. This court specializes in cases related to patent infringement, validity, inventorship, and related matters. Once an appeal is filed, it is usually docketed within about 7 to 10 days. Subsequently, the parties are required to submit briefs according to the court’s schedule, outlining their arguments. Typically, the appealing party submits first, followed by the appellee, and then any reply briefs. These cases are generally heard by a panel of three judges, with each side allotted 15 minutes for oral argument. After oral arguments, the panel votes on the outcome of the appeal and usually issues a written opinion explaining its reasoning. The process from filing the appeal to a decision by the court typically takes about 11 months. If a party wishes to seek further review, they can file a petition for an en banc hearing, where the case is reviewed by all active judges of the court, although this is relatively rare.

In the practical handling of patent infringement cases, the vast majority (over 90%) of disputes do not proceed to the final stages of trial. Instead, parties often opt for settlement to resolve their disputes. A settlement is a mutually agreed-upon contract designed to end litigation by stipulating specific actions. Although settlements usually do not provide a definitive judgment on whether the defendant's actions infringed a valid patent, they are seen as an effective way to avoid the high costs and uncertainties of trial and appellate processes.

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In many cases, the outcome of a settlement may be less than what the parties initially hoped for, but it offers a solution that mitigates risks and conserves resources for both sides. Additionally, settlements can sometimes be facilitated through court-supported alternative dispute resolution methods, such as mediation, early neutral evaluation, or arbitration. These methods provide a structured environment for the parties to negotiate a resolution, often with the assistance of a neutral third party, and can be more efficient and less adversarial than a full trial.