New Zealand is a constitutional monarchy with a parliamentary democracy, although its constitution is not codified. Elizabeth II is the queen of New Zealand and thus the head of state. The queen is represented by the governor-general, whom she appoints on the advice of the prime minister. The governor-general can exercise the Crown's prerogative powers, such as reviewing cases of injustice and making appointments of ministers, ambassadors, and other key public officials, and in rare situations, the reserve powers (e.g. the power to dissolve parliament or refuse the royal assent of a bill into law). The powers of the monarch and the governor-general are limited by constitutional constraints, and they cannot normally be exercised without the advice of ministers.