In political science, the initiative (also known as popular or citizen's initiative) provides a means by which a petition signed by a certain minimum number of registered voters can force a public vote on a proposed statute, constitutional amendment, charter amendment or ordinance. It is a form of direct democracy.

The initiative may take the form of either the direct or indirect initiative. Under the direct initiative, a measure is put directly to a vote after being submitted by a petition. Under the indirect initiative, a measure is first referred to the legislature, and then only put to a popular vote if not enacted by the legislature. In United States usage, a popular vote on a specific measure is referred to as a referendum only when originating with the legislature. Such a vote is known, when originating in the initiative process, as an "initiative," "ballot measure" or "proposition."

The initiative is only available in a certain minority of jurisdictions. It has long been widely used in Switzerland, both at federal and cantonal level. Provision for the initiative was included in the 1922 constitution of the Irish Free State, but was hastily abolished when republicans organised a drive to instigate a vote that would abolish the Oath of Allegiance. The intiative also formed part of the 1920 constitution of Estonia.