ACT OF STATE, a term in law which may be generically described as an act of the Crown, or of some officer whose act is ratified by the Crown, which the courts will treat as conclusive and binding on them in any litigation before them. Such a defence or plea in bar can never be raised by the Crown against the subject except in respect of the exercise of the prerogative in international relations. For a full exposition of the subject, see STATE, ACT OF; and STATE SUCCESSION.