This article deals with the military command/theatre known as the South West Pacific Area. The same name is occasionally used in a purely geographical sense. More common collective names for countries in the region include: South Pacific, Oceania, Australasia and South East Asia.

South West Pacific Area (SWPA) was the name given to one of the four major Allied commands in the Pacific theatre of World War II. The SWPA included the Philippines, Borneo, the Dutch East Indies (excluding Sumatra), Australia, the Territory of New Guinea (including the Bismarck Archipelago), the western part of the Solomon Islands and some neighbouring territories, between 1942 and 1945.

The name "South West Pacific Area" appears to have originated in British military circles in 1941, purely in reference to British forces under the short-lived American-British-Dutch-Australian Command (ABDA). The rapid Japanese advance through the Dutch East Indies effectively divided the "ABDA Area" in two, and in late February 1942, ABDA was wound up at the recommendation of its commander, the British General Archibald Wavell, who — as Allied commander in India — retained responsibility for Allied operations in Sumatra, Singapore, Malaya, Thailand and Burma.

On March 24 1942, the newly-formed British-US Combined Chiefs of Staff issued a directive designating the Pacific theater an area of American strategic responsibility. Six days later the US Joint Chiefs of Staff (JCS) divided the Pacific theater into three areas: the Pacific Ocean Areas (POA), the Southwest Pacific Area (SWPA), and the South East Pacific Area . Therefore most of the Pacific Ocean and its islands fell under a separate Allied command, Pacific Ocean Areas, headed by US Admiral Chester Nimitz.

The Allied commander in the Philippines, General Douglas MacArthur was elevated to the post of Supreme Allied Commander South West Pacific Area. As the Japanese surrounded US and Filipino forces in the Philippines, MacArthur was ordered by US President Franklin D. Roosevelt to leave his headquarters on Bataan Peninsula, near Manila, and to relocate to Melbourne, Australia. As a result, for most of 1942, MacArthur commanded more Australians than US personnel. He also commanded a small number of Dutch forces which had retreated to Australia. Later in the war, some British and other Allied forces also came under MacArthur's command.

One result of the division of the Pacific theatre into two separate commands was that each competed for scarce resources in an economy-of-force theater, and each was headed by a commander in chief (CINC) from a different service. In particular, the division of the Solomons caused problems, since the battles of the Solomon Islands campaign in 1942–1943 ranged over the whole region, with the main Japanese bases in SWPA and the main Allied bases in POA.

MacArthur later moved his headquarters north to Brisbane, Australia.