Australian Capital Territory Legislative Assembly (or, more formally and fully, the Legislative Assembly for the Australian Capital Territory) is the unicameral legislature of the Australian Capital Territory (ACT). It sits in the Legislative Assembly Building located on Civic Square, close to the centre of the city of Canberra.

It was created by four acts of the Commonwealth Parliament in 1988, including the Australian Capital Territory (Self-Government) Act 1988. The first election was held in March 1989 and the assembly first sat on 11 May that year. Until this point, the ACT had been directly administered by the Commonwealth Government. An elected body of the same name had existed for some years prior to 1988, however it had no executive power and its principal function was to advise the Commonwealth on matters relating to the Territory.

The Legislative Assembly has 17 members, elected for four-year terms by the Hare-Clark system, a variation of the Single Transferable Vote form of proportional representation. The 17 members come from three constituencies - Brindabella and Ginninderra, which have five members, and Molonglo, which has seven members. The Assembly was originally elected by a modified d'Hondt system, but a 1992 referendum supported the Hare-Clark method, and this was introduced in 1993.

Members of the Legislative Assembly vote to elect a Chief Minister - in practice, the leader of whichever party can form government. The Chief Minister, in turn, selects up to five ministers to form a cabinet. The leader of the second-largest party in the assembly usually becomes the Leader of the Opposition.

The Assembly is unique in terms of Australian states and territories, as the ACT has neither a Governor nor an Administrator.

Election dates for the Assembly are fixed in legislation, with elections held in October every four years. Elections are always held on Saturdays. Until 1997, elections were held in February. They are now held in October. The term of the Assembly was increased in 2004 from three to four years.

As with the Northern Territory Legislative Assembly, the ACT Assembly lacks the full powers of a state legislature. As a result, legislation passed by the Assembly can be overruled by a Commonwealth act of Parliament or by the Governor-General acting on the advice of the Commonwealth government. Although this is rare in practice, the Civil Unions Act, which allowed same-sex couples to enter into "civil unions," was overruled following concerns that the civil unions mimicked marriage. In July 2006, the federal Government again threatened the ACT Stanhope Government to overrule their anti-terror legislation, which was not consistent with other state laws. The Commonwealth also retained control of the Territory's justice system until handing it over to the Assembly in 1992. The Assembly assumes many of the functions of a local council, as it covers such a small area, and the city of Canberra has no other local government.