The Prime Minister of the Commonwealth of Australia is the head of government in Australia. The individual who holds the office is the most senior Minister of the Crown, the leader of the Cabinet and the chairperson of the National Security Committee. The office is not mentioned in the Constitution of Australia and exists only through an unwritten political convention and tradition. Despite this, in practice it is the most powerful political position in Australia. The individual who holds the office is commissioned by the Governor-General of Australia.