A plaintiff (Π in legal shorthand) is the party who initiates a lawsuit (also known as an action) before a court. By doing so, the plaintiff seeks a legal remedy. If this search is successful, the court will issue judgment in favor of the plaintiff and make the appropriate court order (e.g., an order for damages). "Plaintiff" is the term used in civil cases in most English-speaking jurisdictions, the notable exceptions being England and Wales, where a plaintiff has, since the introduction of the Civil Procedure Rules in 1999, been known as a "claimant" and Scotland, where the party has always been known as the "pursuer". In criminal cases, the prosecutor brings the case against the defendant, but the key complaining party is often called the "complainant".
In some jurisdictions, a lawsuit is commenced by filing a summons, claim form or a complaint. These documents are known as pleadings, that set forth the alleged wrongs committed by the defendant or defendants with a demand for relief. In other jurisdictions, the action is commenced by service of legal process by delivery of these documents on the defendant by a process server; they are only filed with the court subsequently with an affidavit from the process server that they had been given to the defendant according to the rules of civil procedure.
In most English-speaking jurisdictions, including Hong Kong, Nigeria, Australia (except in federal jurisdiction), Canada and the United States, as well as in both Northern Ireland and the Republic of Ireland, the legal term "plaintiff" is used as a general term for the party taking action in a civil case.
The word plaintiff can be traced to the year 1278, and stems from the Anglo-French word pleintif meaning "complaining". It was identical to "plaintive" at first and receded into legal usage with the -iff spelling in the 15th century.
A plaintiff identified by name in a class action is called a named plaintiff.
In most common-law jurisdictions, the term "claimant" used in England and Wales since 1999 (see below) is used only in specific, often non-judicial contexts.