In a lawsuit, the plaintiff is the party who files the case and the defendant is the party being sued. That is the basic difference between a plaintiff and a defendant, and it drives almost everything else: who writes the first document, who has to answer it, who must prove the claim, and who wins if the evidence comes out even. The rest is detail built on that split.
What the Plaintiff Does
The plaintiff is the person, business, or organization claiming they were harmed. To start the case, they file a complaint laying out what happened, what law or duty was broken, and what they want the court to do.1Legal Information Institute. Complaint The complaint is delivered to the defendant together with a summons, the court’s formal notice that a lawsuit has been filed.
What the plaintiff asks for depends on the dispute. Usually it is money for losses like medical bills, lost wages, or property damage. Sometimes it is an injunction, which is a court order telling the other side to do something or to stop doing something.2Legal Information Institute. Injunction A business might seek an injunction to stop a former employee from sharing trade secrets; a neighbor might seek one to halt construction that violates zoning rules.
The plaintiff also has to beat the clock. Every civil claim has a statute of limitations, a deadline for filing. Miss it and the court will dismiss the case no matter how strong the evidence is. Deadlines vary by claim type and jurisdiction, from as little as a year to well over a decade, and claims against government entities often carry even shorter pre-suit notice periods.
What the Defendant Does
The defendant is on the receiving end. Once served with the complaint and summons, the first obligation is to respond within the time the rules allow. In federal court that deadline is 21 days from the date of service.3Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections A defendant who waived formal service gets 60 days, and government defendants get 60 days as well.
The response is called an answer. In it, the defendant goes through each allegation in the complaint and either admits it, denies it, or states they lack enough information to respond. This sounds like a formality, but anything the defendant admits is treated as established fact for the rest of the case, so sloppy answers cause real damage later.
A defendant can also challenge the lawsuit itself before answering, by filing a motion to dismiss. Federal rules let the defendant argue, among other things, that the court lacks jurisdiction, that the plaintiff filed in the wrong court, or that the complaint fails to describe a valid legal claim even assuming everything in it is true.3Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections A successful motion to dismiss can end the case before the defendant ever addresses the substance.
Ignoring the lawsuit is not an option. When a defendant fails to respond or defend, the plaintiff can ask the clerk to enter a default and then seek a default judgment.4Legal Information Institute. Federal Rules of Civil Procedure Rule 55 – Default and Default Judgment The defendant loses without ever making a case.
Who Has to Prove What
The structural advantage the defendant holds is that they do not have to prove anything at the start. The plaintiff carries the burden of proof. They must present enough evidence to convince the judge or jury that their version of events is correct.5Legal Information Institute. Burden of Proof The defendant’s job is to poke holes in that case.
In most civil lawsuits, the standard is preponderance of the evidence, meaning the plaintiff only needs to show the claim is more likely true than not.5Legal Information Institute. Burden of Proof Picture tipping a scale slightly. If the evidence comes out perfectly balanced, the plaintiff loses. A tie goes to the defendant.
Some civil claims demand a higher standard called clear and convincing evidence. It applies to fraud allegations, claims for punitive damages, and certain other contexts where courts want more certainty before imposing serious consequences. It sits between the ordinary civil standard and the beyond a reasonable doubt standard used in criminal trials.
When the Defendant Has to Prove Something
There is an important exception to the burden rule. If the defendant raises an affirmative defense, the defendant has to prove it. An affirmative defense does not dispute what the plaintiff says happened. It argues that even if every allegation is true, the defendant still should not be held liable.
Federal rules list nearly twenty affirmative defenses. Common ones include:6Legal Information Institute. Federal Rules of Civil Procedure Rule 8 – General Rules of Pleading
- Statute of limitations: the plaintiff waited too long to file.
- Contributory negligence: the plaintiff’s own actions contributed to the injury.
- Assumption of risk: the plaintiff knowingly accepted the danger that caused the harm.
- Fraud: the plaintiff’s own fraudulent conduct undermines the claim.
- Accord and satisfaction: the parties already settled the dispute.
- Duress: the defendant was forced or coerced into the conduct at issue.
Affirmative defenses must be included in the answer.6Legal Information Institute. Federal Rules of Civil Procedure Rule 8 – General Rules of Pleading Waiting until trial to spring one is a good way to have the court refuse to consider it.
What Both Sides Owe Each Other
Once the case is underway, both parties have to share information through discovery. This is where the roles even out. Whichever side you are on, you are required to hand over relevant evidence, including evidence that hurts your own case.
Under federal rules, both parties must make initial disclosures within 14 days of their first planning conference, without being asked. These include:7Legal Information Institute. Federal Rules of Civil Procedure Rule 26 – Duty to Disclose
- Names and contact information of people likely to have relevant knowledge, and the topics they know about.
- Copies or descriptions of documents and electronic data that support the party’s claims or defenses.
- A breakdown of each category of damages claimed, with the supporting materials.
- Any insurance policy that could cover part or all of a potential judgment.
After the initial exchange, both sides can request additional documents, send written questions called interrogatories, and take depositions, which are recorded question-and-answer sessions under oath. The plaintiff uses discovery to build the case; the defendant uses it to find weaknesses. Neither side can hide behind an unfinished investigation to withhold what they already have.7Legal Information Institute. Federal Rules of Civil Procedure Rule 26 – Duty to Disclose
When the Labels Blur
Plaintiff and defendant are not always fixed. A defendant who believes the plaintiff actually owes them something can file a counterclaim, which is essentially a lawsuit filed inside the existing one.8Legal Information Institute. Federal Rules of Civil Procedure Rule 13 – Counterclaim and Crossclaim The original defendant becomes a counter-plaintiff on that claim, and the original plaintiff has to defend against it.
If the defendant’s claim arises from the same events as the lawsuit, it is compulsory, and the defendant must raise it or lose the right to sue on it later.9Legal Information Institute. Counterclaim A claim about an unrelated dispute is permissive; the defendant can bring it for efficiency but is not required to.
On the plaintiff’s side, a case can expand into a class action when one person’s claim is shared by a large group. Federal rules require that the class be large enough that individual lawsuits would be impractical, that the claims share common legal questions, and that the representative plaintiffs can adequately protect the group’s interests.10Legal Information Institute. Federal Rules of Civil Procedure Rule 23 – Class Actions Product liability and consumer fraud cases often take this form.
Different Courts Use Different Words
Everything above is civil litigation, where one private party sues another. Other proceedings use different labels, and the differences matter.
In a criminal case, the government brings the charges, not a private person. The initiating party is the prosecutor and the person accused is the defendant.11U.S. Department of Justice. Legal Terms Glossary A crime victim does not decide whether charges are filed; that is the prosecutor’s call. The victim may be a witness but is not a party.
In family law matters like divorce or custody, the parties are the petitioner and the respondent. The petitioner files the initial petition and the respondent answers it. The roles track plaintiff and defendant, but the different vocabulary reflects that family courts often handle disputes less adversarially.
On appeal, the party who lost at trial and asks a higher court to review the decision is the appellant. The party defending the trial court’s ruling is the appellee, sometimes called the respondent.12Legal Information Institute. Appellant Either the original plaintiff or the original defendant can end up as the appellant, depending on who lost below.
What Each Side Pays For
The costs of a lawsuit hit the two sides differently. The plaintiff pays the filing fee to open the case, which in federal court currently runs $405 for a standard civil action. The plaintiff also pays to have the defendant formally served, which can be minimal if a friend delivers the papers or several hundred dollars with a professional process server.
After that, both sides pay for discovery: document collection, deposition transcripts, and expert witnesses, with expert fees often running into the thousands per witness. Under the American Rule, each side pays its own attorney regardless of who wins. The losing side does not automatically owe the winner’s legal bills unless a specific statute or contract says otherwise.
Those costs shape how cases actually end. The large majority of civil lawsuits settle before trial, often through mediation or arbitration, because both sides recognize that pushing a case through trial can cost more than the dispute itself is worth.