Armed conflict between states in Southeast Asia has been relatively rare, especially since 1979. The most recent exception to this pattern was a border dispute between Cambodia and Thailand that turned violent in 2008 and remained militarized for more than three years. Existing studies of this long-standing conflict have concentrated on explaining the upsurge in violence between 2008 and 2011, but have tended to ignore that fighting was quickly contained each time clashes occurred. This article provides a different perspective and asks how the dispute was managed short of large-scale armed violence. To answer this question, the author adopts an agency-focused perspective that emphasizes the role of critical actors who worked to de-escalate the conflict. Based on field research conducted in Cambodia and Thailand, as well as consulting primary and secondary sources, the author adopts a historical narrative that revisits critical periods from the 1950s onwards and argues that relevant actors in both Cambodia and Thailand had long-standing incentives to avoid escalating the conflict. Two elements were critical: first, crucial actors including Cambodian and Thai bureaucrats, diplomats and members of the security and intelligence services developed an understanding of the problems inherent in defining their land border; and second, the establishment of personal contacts, even in the context of antagonistic relations. Together, these factors created possibilities for Cambodia and Thailand to cooperate in managing conflict and increased the willingness of both sides to exercise self-restraint.