否决权（Veto），指政治上一种片面否定决策或决议的权力，尤其是立法。

A veto – Latin for "I forbid" – is the power (used by an officer of the state, for example) to unilaterally stop an official action, especially the enactment of legislation. A veto can be absolute, as for instance in the United Nations Security Council, whose permanent members (China, France, Russia, United Kingdom, United States of America) can block any resolution. Or it can be limited, as in the legislative process of the United States, where a two-thirds vote in both the House and Senate may override a Presidential veto of legislation. A veto gives power only to stop changes, not to adopt them (except for the rare "amendatory veto"). Thus a veto allows its holder to protect the status quo.