The questions of how and when the Cold War manifested itself in Southeast Asia are here examined through the perceptions of Britain and Australia to regional and global events from 1945 to 1950. Both had major stakes in the eventual results of the local contentions in Southeast Asia, as well as in the global effects of great power rivalry. Yet even for these powers, determining when they believed the Cold War came to Southeast Asia is dependent on the definition adopted. By 1946, there was already recognition of entrenched ideological conflict in Southeast Asia, and that this threatened Western interests. In 1947, there was recognition of connections between the local communist parties and the ‘global designs’ of the Soviet Union. In 1948, there was the outbreak of armed violence in Burma, Malaya and Indonesia, though there was no evidence of direct Soviet involvement in these. Ultimately, however, it was the establishment of the PRC in 1949 (as a major regional communist power), in tandem with plans by non-communist states to coordinate policy against communism, which was seen as marking the arrival of fully-fledged Cold War in Southeast Asia.