The difference between a plaintiff and a defendant comes down to who started the lawsuit and who has to answer for it. The plaintiff files the case and carries the burden of proving it. The defendant is the party being sued and has to respond, defend, or risk losing by default. Those two labels shape every stage that follows: who files first, who proves what, which deadlines apply, and what happens if someone goes silent.
What the Plaintiff Does
The plaintiff starts a lawsuit by filing a complaint with the court. The complaint spells out what the defendant allegedly did or failed to do, why it caused harm, and what the plaintiff wants, usually money damages or a court order telling the defendant to stop doing something.
Filing also means accepting the burden of proof. In most civil cases, the plaintiff has to show that their version of events is more likely true than not. This standard is called “preponderance of the evidence,” and it works like tipping a scale just past the midpoint. If the plaintiff’s evidence doesn’t reach that point, the defendant wins without having to present a defense of their own.
After filing, the plaintiff is responsible for making sure the defendant actually receives the paperwork. Under federal rules, the summons and complaint must be delivered to the defendant personally, left at their home with a responsible adult who lives there, or given to an authorized agent.1Cornell Law School Legal Information Institute. Federal Rules of Civil Procedure Rule 4 – Summons The plaintiff can also ask the defendant to waive formal service by mail, which trims costs and gives the defendant extra time to respond. Fail to serve the defendant within 90 days, and the court can dismiss the case.
What the Defendant Does
The defendant is the person, business, or organization accused of causing the harm. Their role begins the moment they’re formally served. From that point, the clock starts. In federal court, a defendant generally has 21 days to file a response.2Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections: When and How Presented If the defendant waived formal service, that deadline stretches to 60 days. State court deadlines vary, so check local rules.
The response is usually an “answer.” The defendant goes through each allegation in the complaint and admits it, denies it, or says they don’t have enough information to respond. The defendant can also raise affirmative defenses, which are legal reasons the plaintiff should lose even if the underlying facts are true. An expired statute of limitations is a common example.
Ignoring the lawsuit is the single worst move a defendant can make. If the response deadline passes with nothing filed, the court can enter a default judgment, essentially handing the plaintiff a win without a trial. That judgment is real and enforceable. The plaintiff can use it to garnish wages or seize bank accounts. Courts sometimes set aside a default judgment when the defendant has a good reason for missing the deadline, but “I didn’t think it was serious” rarely qualifies.
How the Burden of Proof Separates the Two Sides
The plaintiff has to prove the case. The defendant does not have to prove innocence or disprove anything. If the plaintiff’s evidence doesn’t carry the day, the defendant wins by default of the proof, not by presenting a stronger story. Many defendants and even some plaintiffs misunderstand this. A defendant can lose a case they would have won simply by failing to show up. A plaintiff can lose a case they should have won simply because the admissible evidence doesn’t tip the scale.
Criminal Cases Work Differently
If you’re trying to apply these labels to a criminal case, only half of them fit. The accused person is still called the defendant. But there is no private plaintiff. The government brings the case through a prosecutor.3United States Courts. Criminal Cases In federal court that’s the U.S. Attorney; in state court it’s usually the district attorney or state’s attorney. A crime victim may testify as a witness but does not control the case, which is why criminal matters are styled “United States v. Smith” or “People v. Smith.”
The burden is also much higher. A civil plaintiff needs to show their claims are more likely true than not. A criminal prosecutor must prove guilt “beyond a reasonable doubt,” reflecting the fact that a defendant’s liberty is on the line.3United States Courts. Criminal Cases
When the Roles Shift or Multiply
Plaintiff and defendant aren’t always fixed positions. Procedural rules let parties switch roles or bring in new ones.
Counterclaims
A defendant who believes the plaintiff also caused them harm can file a counterclaim, essentially a lawsuit within the lawsuit. For that claim, the original defendant goes on offense and the original plaintiff plays defense. Federal rules split counterclaims into two kinds. A compulsory counterclaim arises out of the same events as the plaintiff’s original claim, and the defendant must raise it in that case or lose it for good.4Legal Information Institute. Federal Rules of Civil Procedure Rule 13 – Counterclaim and Crossclaim A permissive counterclaim involves a separate dispute and can be filed later as its own case.
Cross-Claims and Joinder
When several defendants are named in the same lawsuit, one defendant can file a cross-claim against another if it arises from the same underlying events. Picture a multi-car accident where two drivers are both sued; one may cross-claim against the other, arguing the other driver was actually at fault.
Joinder is how parties get added. Multiple plaintiffs can join in one action, or multiple defendants can be brought in, as long as the claims arise from the same events and share common questions of law or fact.5Cornell Law School – Legal Information Institute. Federal Rules of Civil Procedure Rule 20 – Permissive Joinder of Parties That’s where terms like “co-plaintiff” and “co-defendant” come from.
On Appeal
If the case goes up to a higher court, the labels change again. The party who files the appeal becomes the appellant, sometimes called the petitioner. The party defending the lower court’s decision becomes the appellee, or respondent. Either the original plaintiff or the original defendant can be the appellant. It depends entirely on who lost and wants the decision reviewed. Appeals aren’t retrials. The appellant generally has to show that the trial judge made a legal error, not simply that the jury got the facts wrong.
Deadlines Each Side Faces
Every civil claim has a statute of limitations, a window during which the plaintiff must file suit or permanently lose the right. Personal injury claims commonly run two to four years depending on the state. Contract disputes often get longer windows. Once the deadline passes, the strength of the evidence no longer matters; the court will dismiss the case. In limited circumstances the clock can be paused, a concept called tolling, but the rules vary significantly by state.
The defendant’s main deadline is the response window after being served. Miss it, and default judgment is on the table.
Representing Yourself as Either Party
Plaintiffs and defendants both have the right to represent themselves without hiring a lawyer. Federal law explicitly allows parties in all federal courts to handle their own cases, and state courts generally extend the same right.6Office of the Law Revision Counsel. 28 US Code 1654 – Appearance Personally or by Counsel A person who does this is called a “pro se” litigant. The court won’t make it easy. Pro se litigants are held to the same procedural rules, filing deadlines, and evidence standards as attorneys. One limitation worth knowing: corporations and other business entities generally cannot represent themselves and must hire a lawyer, because an entity can only act in court through a licensed attorney.