In a court of law, a party's claim is a counterclaim if one party asserts claims in response to the claims of another. In other words, if a plaintiff initiates a lawsuit and a defendant responds to the lawsuit with claims of their own against the plaintiff, the defendant's claims are "counterclaims."

Examples of counterclaims include:

In U.S. federal courts, counterclaims can arise on various occasions, including e.g.:

Dependent upon the location of where the lawsuit was originated, the defending party has a period of time to file a countersuit, also known as a counterclaim, against the claiming party. This is a direct claim from the defending party against the party who initiated the lawsuit for concurrent claims, including being wrongfully sued.

A crossclaim is a pleading made against a party who is a co-defendant or co-plaintiff. A crossclaim is against anyone who is "on the same side of the lawsuit". An example of this is a manufacturing company who ships their product through a third-party transportation company to the buyer. Upon the products being inspected by the buyer, the buyer finds that the product has been damaged in shipping and refuses to pay. If the manufacturer sued the buyer, the buyer would serve an answer with a denial that the buyer owed money to the manufacturer and a crossclaim to the shipping company to compensate for the damages.

Under the Federal Rules of Civil Procedure (FRCP), counterclaims are either compulsory or permissive.

Permissive counterclaims comprise "any claim that is not compulsory." Such claims may be brought, but no rights are waived if they are not. Courts rarely give permissive counterclaims the necessary supplemental jurisdiction to be brought.^{[citation needed]}

A claim is a compulsory counterclaim if, at the time of serving the pleading,