The Free World Military Assistance Forces (FWMAF), also known as the Free World Military Forces (FWMF) and the Free World Forces (FWF), was the group of allied nations who sent troops to fight in the Vietnam War under the FWMAF banner, assisting South Vietnam against North Vietnam and the Viet Cong (VC). Together with South Vietnamese, the FWMAF were often referred to as the "Allies". It did not include anti-communist armies in Laos and Cambodia that also supported South Vietnam and fought native communists supported by North Vietnam.

On 23 April 1964, United States President Lyndon B. Johnson called for "more flags" to support South Vietnam. Also in April the Ministerial Council of the Southeast Asia Treaty Organization (SEATO) issued a communique declaring the defeat of the VC essential to Southeast Asia's security and underscoring the necessity for SEATO nations to fulfill their treaty obligations.

In a meeting at the White House on 1 December 1964, it was resolved that aid be sought from "key allies". Thailand was to be asked to support the U.S. and intensify its own counterinsurgency efforts in Thailand. Prime Minister Harold Wilson of the United Kingdom was to be briefed and his support sought. William P. Bundy of the U.S. State Department was to ask Australia and New Zealand for additional help as well as consideration of sending small combat units. The Philippines were to be asked for a commitment of approximately 1,800 men. Assistance from South Korea was not discussed at the meeting. Aside from tentative probes of the attitudes of the governments of Australia and New Zealand, no effort was being made to secure combat troops for South Vietnam, but rather economic assistance, military advisers, civil affairs personnel and humanitarian aid was sought.

The usual procedure was to have the American embassies in Europe, Asia, and Latin America discuss the subject of aid for South Vietnam with the host countries. Military Assistance Command, Vietnam (MACV) and the U.S. Operations Mission prepared a list of the kind of aid desired. When a country agreed to provide some assistance the U.S. government then informed the South Vietnamese government, which in turn made a formal request for aid from the country.

In January 1965, as the U.S. became more actively engaged in the war, the search for more flags was intensified and the U.S. began to seek combat units.

On 6 April 1965, the decision to seek Free World combat troops was confirmed and embodied in National Security Action Memorandum 328. The State Department was to explore with the South Korean, Australian and New Zealand governments the possibility of rapidly deploying combat elements of their armed forces in conjunction with additional U.S. deployments. Both Australia and South Korea had already on 3 April 1965 indicated informally their willingness to send combat troops.

In June 1965, the first FWMAF troops arrived in South Vietnam with the 1st Battalion, Royal Australian Regiment deployed to Bien Hoa Air Base under the operational control of the U.S. 173rd Airborne Brigade. They would be joined in July by the 161st Field Battery, Royal New Zealand Artillery.

In September 1965, the South Korean Capital Division and 2nd Marine Brigade were landed at Qui Nhon.