Corresponding to the global proliferation of inter-state activities at the regional level since the end of the Cold War, Eurasia has experienced a surge of regional agreements and organizations. Since the dissolution of the Soviet Union, more than 29 regional organizations (ROs) with significant membership and agenda overlap have emerged. These organizations differ significantly in terms of institutional design. Organizations that were created in the 1990s and early 2000s display very limited or no pooling of authority and low to moderate delegation. Regional organizations that were established during the past decade show pronounced delegation and median pooling. A mapping based on formal treaty analysis shows a general deepening of regional integration over time. It also reveals three phases of Eurasian regionalism with distinct integration dynamics and goals. Especially the third phase is surprising, as we do not only witness the increase of political authority of ROs, but also a more consequent implementation of agreements and the introduction of supranational elements. This deepening of regionalism is puzzling in light of 1) the rather recent independence of the Eurasian states and their colonial past under Russian domination, 2) the level of autocracy in the region, and 3) the presence of a regional hegemon, which has moreover recently experienced an authoritarian backlash. Relying on the concept of political authority, the first part of this paper gives an overview of the development of formal regional integration in Eurasia during the past 25 years. The second part of the paper asks why Russia and the smaller Eurasian states go along with increasing authority transfers to ROs. Based on a series of elite interviews conducted in Russian in February and March 2017, potential drivers of Eurasian regionalism are explained, with particular attention to Russian motives. The paper concludes with an outlook on avenues for future research.