In United States law, a defendant is any person who is required to answer the complaint of a plaintiff in a civil suit or any person who has been named in a criminal information or criminal complaint and stands accused of violating a criminal statute. A defendant in a civil action usually makes his or her first court appearance, voluntarily, in response to a summons whereas a defendant in a criminal case is usually taken into custody by a peace officer and brought before a court, pursuant to an arrest warrant. The actions of a defendant, and their counsel, is known as the defence.

A respondent is the parallel term used in a proceeding which is commenced by petition.

Historically, a defendant in a civil action could also be taken into custody pursuant to a writ of capias ad respondendum and forced to post bail before being released from custody. However, a modern day defendant in a civil action is usually able to avoid most (if not all) court appearances if he or she is represented by a lawyer whereas a defendant in a criminal case (particularly a felony) is usually obliged to post bail before being released from custody and must be present at every stage thereafter of the proceedings against him or her.