During the Third Indochina War (1979-1991), the ideological alignments of involved parties differed from those during the Second Indochina War, also known as the Vietnam War. Whereas the Second Indochina War pitted communists squarely against non-communists and anti-communists, the Third Indochina War was more complicated and less ideological or political, with communists often fighting against other communists due to the Sino-Soviet ideological split. The enemy of one's enemy was frequently viewed as a friend, often leading to unlikely alliances not rooted in ideological or political similarities. In this article, I argue that it is important to consider the unlikely alliances that emerged during the Third Indochina War by focusing on the particular cross-border interactions and conflicts between communists and non-communists that occurred in the Emerald Triangle, the tri-border region between Laos, Cambodia and Thailand. Focusing particularly on the Lao insurgent perspective, I consider how Lao anti-communist insurgents, the Khmer Rouge, the Communist Party of Thailand, other armed groups, and the Thai military participated in transnational collaboration in this region during the Third Indochina War. In particular, based largely on Lao-language interviews with key figures in the Lao insurgency conducted for over a decade, I examine how Lao insurgents interacted with Khmer Rouge to oppose a common enemy, communist Vietnam and their allies, the People's Republic of Kampuchea and the Lao People's Democratic Republic, and how the Thai military supported them, but only insofar as it enabled them to maintain control over security inside Thailand.