The Twenty-seventh Amendment (Amendment XXVII, also known as the Congressional Compensation Act of 1789) to the United States Constitution states that any law that increases or decreases the salary of members of Congress may take effect only after the next election of the House of Representatives has occurred.

The Twenty-seventh Dynasty of Egypt (notated Dynasty XXVII, alternatively 27th Dynasty or Dynasty 27), also known as the First Egyptian Satrapy, was a satrapy of the Achaemenid Empire between 525 and 404 BC.

The Twenty-seventh Amendment of the Constitution Act 2004 (previously bill no. 15 of 2004) amended the Constitution of Ireland to limit the constitutional right to Irish citizenship of individuals born on the island of Ireland to the children of at least one Irish citizen and the children of at least one parent who is, at the time of the birth, entitled to Irish citizenship.