In some legislatures, a casting vote may be exercised however the presiding officer wishes. An example is the Vice President of the United States, who may exercise his casting vote in the Senate according to his party affiliation or according to his own personal beliefs. By virtue of the Vice President's casting vote, when the Senate as elected is equally divided between two parties, the Vice President's party automatically becomes the official majority party in the Senate. The exercise of the Vice President's casting vote has become increasingly rare throughout American history as the size of the Senate has grown from 26 to 100 and ties have become less probable.
In some other legislatures, by contrast, a casting vote can only be exercised according to strict rules or conventions. For example, the Speaker of the British House of Commons is expected to vote to allow further discussion, if this is possible, and otherwise to vote against the proposal concerned.
Some countries have abandoned the concept of a casting vote. For example, the Speaker of the New Zealand House of Representatives formerly held a casting vote similar that of the Speaker of the British House of Commons. Today, however, the Speaker simply votes as an ordinary member, and since an outright majority is necessary for a bill to pass, a tie is considered to be a defeat.