An opposing party is the person, business, or government entity on the other side of your legal dispute. Every lawsuit and every criminal prosecution has at least two sides with conflicting interests, and the one working against your position is your opposing party. The definition is simple, but who qualifies can shift as a case moves along, and specific rules govern how you deal with them.
Who Your Opposing Party Is in Civil and Criminal Cases
In a civil lawsuit, the opposing party is whoever you’re in a legal dispute with. That might be a former spouse, a neighbor, a landlord, a competitor, a nonprofit, a local government, or a Fortune 500 corporation. One side claims the other caused harm or broke an agreement; the other side defends against the claim.
Criminal cases work differently. If you’re a criminal defendant, your opposing party is always the government. Federal cases are styled “United States v. [Defendant].” State cases read “State v.,” “People v.,” or “Commonwealth v.” depending on the jurisdiction. Prosecutors carry the burden of proving guilt beyond a reasonable doubt, and the Sixth Amendment guarantees the accused the right to be informed of the charges, to confront witnesses, to compel favorable testimony, and to have counsel.1Library of Congress. Right to Confront Witnesses Face-to-Face You don’t choose your opposing party in a criminal case the way a civil plaintiff chooses who to sue. The government decides whether to charge you, and once it does, the full weight of the prosecution is on the other side.
The Labels You’ll See on Court Papers
The names attached to opposing parties change with the type and stage of the case:
- Plaintiff and defendant. In a standard civil lawsuit, the party filing the case is the plaintiff and the party being sued is the defendant.
- Petitioner and respondent. In cases built around a formal request rather than a damages claim — divorce, immigration, administrative appeals — the party asking is the petitioner and the other side is the respondent.
- Appellant and appellee. When a losing party appeals, that party becomes the appellant. The winner below, defending the original outcome, is the appellee.
- Prosecution and defendant. In criminal cases, the government side is “the prosecution” or “the People,” and the accused is the defendant.
The label tells you who has to prove what. A plaintiff or petitioner carries the initial burden. A defendant or respondent challenges those claims. An appellant has to show the trial court made a legal error worth correcting.
How Someone Formally Becomes Your Opposing Party
Filing a lawsuit doesn’t automatically make a defendant your opposing party in the eyes of the court. The defendant has to be formally notified through service of process. In federal court, once the plaintiff files a complaint, the clerk issues a summons that names the parties, states when the defendant must respond, and warns that a failure to respond will result in a default judgment.2Legal Information Institute. Federal Rules of Civil Procedure Rule 4 – Summons The summons and a copy of the complaint are then delivered to the defendant.
Service on an individual within the United States usually means handing the papers directly to that person, leaving them with a responsible adult at the person’s home, or delivering them to an authorized agent. For businesses, service goes to an officer, a managing agent, or someone the company has authorized to accept legal papers.2Legal Information Institute. Federal Rules of Civil Procedure Rule 4 – Summons Anyone at least 18 and not a party to the lawsuit can carry out the service. The plaintiff can also ask the defendant to waive formal service, though the defendant isn’t obligated to agree.
When the Lineup of Opposing Parties Changes
The sides aren’t locked in at the start. Several procedural tools let the configuration shift.
Counterclaims
A defendant who believes the plaintiff actually owes them something can file a counterclaim, reversing the roles for that particular claim. If the counterclaim arises out of the same events as the original lawsuit, filing it is mandatory; skip it and you lose the right to bring it later.3Legal Information Institute. Federal Rules of Civil Procedure Rule 13 – Counterclaim and Crossclaim If it involves an unrelated dispute, the defendant can include it but isn’t required to.
Crossclaims
Sometimes parties nominally on the same side have disputes with each other. A crossclaim is a claim by one defendant against another defendant (or one plaintiff against another plaintiff), as long as it arises from the same underlying events. Two co-defendants in a car accident case, each blaming the other, is the classic example. The crossclaim turns former allies into opposing parties on that specific issue.3Legal Information Institute. Federal Rules of Civil Procedure Rule 13 – Counterclaim and Crossclaim
Third-Party Practice
A defendant can also bring in someone who isn’t yet part of the case. If the defendant believes an outsider is actually responsible for the plaintiff’s losses, the defendant can file a third-party complaint. This has to happen within 14 days of filing the answer, or with the court’s permission afterward.4Legal Information Institute. Federal Rules of Civil Procedure Rule 14 – Third-Party Practice New opposing-party relationships can form between people who had nothing to do with each other when the case started.
What Happens When an Opposing Party Ignores the Case
Being named as an opposing party creates a legal obligation to respond. When a defendant doesn’t file an answer and doesn’t show up, the other side can ask the court to enter a default, which forfeits the defendant’s right to defend. The plaintiff can then seek a default judgment and win the case without the defendant ever participating.5Legal Information Institute. Federal Rules of Civil Procedure Rule 55 – Default; Default Judgment Courts can undo a default for good cause, but the bar rises once an actual judgment has been entered. Ignoring a lawsuit is one of the most expensive mistakes people make.
Getting Information From the Other Side
You don’t have to rely only on your own evidence. The rules force opposing parties to share information through discovery.
In federal court, both sides have to hand over basic information without being asked. Within 14 days of their initial planning conference, each party must disclose the names and contact information of people with relevant knowledge, copies or descriptions of supporting documents and electronic files, a computation of claimed damages with backup materials, and any insurance policy that might cover the judgment.6Legal Information Institute. Federal Rules of Civil Procedure Rule 26 – Duty to Disclose; General Provisions Governing Discovery A party who joins later gets 30 days from being served. You can’t skip your own disclosures because the other side hasn’t made theirs or because you haven’t finished investigating.
Beyond those automatic disclosures, each side can send the other written questions called interrogatories. Federal rules cap these at 25 per party, including subparts, and the opposing party has 30 days to answer under oath.7Legal Information Institute. Federal Rules of Civil Procedure Rule 33 – Interrogatories to Parties Depositions, document requests, and requests for admissions round out the main discovery tools.
Rules for Communicating With an Opposing Party
If the opposing party has a lawyer, you generally cannot contact that person directly about the case. The “no-contact rule” prohibits a lawyer from communicating about the subject of the lawsuit with someone they know is represented by counsel, unless the other lawyer consents or a court order allows it.8American Bar Association. Rule 4.2 – Communication with Person Represented by Counsel The rule applies even when the represented person starts the conversation. Communication goes through the lawyers.
When an opposing party doesn’t have a lawyer, the rules still require fairness. An attorney dealing with an unrepresented opposing party cannot imply that they are neutral or looking out for both sides. If you’re representing yourself and the other side has counsel, that attorney can talk to you directly but cannot mislead you about their role or your situation. Parties themselves are always free to speak to each other, but anything said can end up as evidence, so most lawyers strongly discourage it once litigation is underway.