While domestic environmental agencies are still responsible for follow up the progress of environmental policy, the context of complex and large-scale environmental problems strongly influence the possibility to fulfill policy objectives. This thesis explores a case of bilateral environmental cooperation carried out by Swedish environmental authorities, to analyze how it contributes to governance and governability of environmental issue areas. Qualitative interviews with concerned actors revealed that bilateral cooperation was perceived to fill specific functions for the governability of environmental issues, complementary to other international cooperation. Key perceived qualities of bilateral cooperation were that it enabled trustful relations on working level and served as a door opener for dialogue. Joint policy development by environmental agency peers and demonstrating successful examples were seen as useful for promoting policy change. Applying a perspective of interactive governance, the thesis highlights that goals and activity selection of the studied bilateral cooperation were formed through interactions between the involved agencies and with partner countries. Bureaucratic structure and discourses on international cooperation constitute important limitations to the development and use of bilateral environmental cooperation. The study recommends governability assessment as a tool for improving design and follow-up of international environmental cooperation. Governability assessment analyzes the role that the interaction, and the interacting organization play in a governing system of an environmental issue area. The thesis adds to previous research on global environmental governance with empirical examples of the role bilateral interactions plays in the governing systems, as well as the specific qualities perceived by actors as crucial to the role. It also provides recommendations on how to further analyze initiatives by actors aiming to exercise environmental leadership in a diverse or fragmented institutional context of global environmental governance.