The Prime Minister of Canada is in charge of the Prime Minister's Office. The Prime Minister also chooses the ministers that make up the Cabinet. The two groups, with the authority of the Parliament of Canada, manage the Government of Canada and the Canadian Armed Forces. The Cabinet and the Prime Minister also appoint members of the Senate of Canada, the judges of the Supreme Court of Canada and federal courts, and the leaders and boards, as required under law, of various Crown Corporations, and selects the Governor General of Canada. Under the Canadian constitution, all of the power to exercise these activities is actually vested in the Monarchy of Canada, but in practice the Canadian monarch (who is the head of state) or their representative, the Governor General of Canada approves them routinely, and their role is largely ceremonial, and their powers are only exercised under the advice of the Prime Minister.
Not outlined in any constitutional document, the office exists only as per long-established convention (originating in Canada's former colonial power, the United Kingdom) that stipulates the monarch's representative, the governor general, must select as prime minister the person most likely to command the confidence of the elected House of Commons; this individual is typically the leader of the political party that holds the largest number of seats in that chamber.[note 1]