The Collective Security Treaty Organization (CSTO) is a collective security organisation of post-Soviet states in which Russia is the dominant partner. Although it has often appeared to analysts to be more developed and eective on paper than in reality, and is frequently overshadowed by other organisations operating fully or partly in the post-Soviet space such as the Shanghai Cooperation Organisation (SCO) or the Eurasian Union, it has proved to be an important, if limited, vehicle for Russian foreign and security policy. The character of its development since the mid-2000s reects Russian political and military predominance within the organisation, but also the growth of concerns shared by Russia and other member states about the twin threats to regional and regime security posed by the situation in Afghanistan and the normatively framed challenges from the West, above all the US. At the same time, the problems surrounding its development and its limited membership reect the limits of Russian material and ideational capabilities when faced with the region’s complex dynamics and the concerns about the threats posed by Russian domination. In this way, the CSTO can be seen as an interesting reection of the capacity and limits of Russian regional hegemony.