An appropriation , also known as supply bill or spending bill, is a proposed law that authorizes the expenditure of government funds. It is a bill that sets money aside for specific spending. In most democracies, approval of the legislature is necessary for the government to spend money.

In a Westminster parliamentary system, the defeat of an appropriation bill in a parliamentary vote generally necessitates either the resignation of a government or the calling of a general election. One of the more famous examples of the defeat of a supply bill was the 1975 Australian constitutional crisis, when the Senate, which was controlled by the opposition, refused to approve a package of appropriation and loan bills, prompting Governor-General Sir John Kerr to dismiss Prime Minister Gough Whitlam and appoint Malcolm Fraser as caretaker Prime Minister until the next election (where the Fraser government was elected).

The House of Commons of Northern Ireland was the lower house of the Parliament of Northern Ireland created under the Government of Ireland Act 1920. The upper house in the bicameral parliament was called the Senate. It was abolished with the passing of the Northern Ireland Constitution Act 1973.