The Australia, New Zealand, United States Security Treaty (ANZUS or ANZUS Treaty) is the military alliance which binds Australia and New Zealand and, separately, Australia and the United States to cooperate on defence matters in the Pacific Ocean area, though today the treaty is understood to relate to attacks worldwide.

The treaty was previously a full three-way defense pact, but following a dispute between New Zealand and the United States in 1984 over visiting rights for nuclear-armed or nuclear-powered ships of the US Navy to New Zealand ports, the treaty may have lapsed between the United States and New Zealand, although it remains separately in force between both those countries and Australia.

The Australia–US alliance under the ANZUS Treaty remains in full force. Heads of defense of one or both nations often have joined the annual ministerial meetings, which are supplemented by consultations between the US Combatant Commander Pacific and the Australian Chief of Defence Force. There are also regular civilian and military consultations between the two governments at lower levels. Annual meetings to discuss ANZUS defense matters take place between the United States Secretary of State and the Australian Minister for Foreign Affairs (AUSMIN). The most recent AUSMIN meeting took place in San Francisco in September 2011.