This paper examines the duality of shared responsibility. The paper argues that shared responsibility is generally regarded as having the potential to address responsibility gaps in situations of concerted action. As such, shared responsibility may be important for global governance in relation to such diverse areas as peace-keeping, climate change, migration, and conservation of natural resources. The paper also argues that the sharing of responsibility can lead to a diffusion of responsibility that makes it more difficult to determine who is responsible for what. Thereby, it can undermine the effectiveness of global governance and moreover generate a new set of responsibility gaps. However, on the basis of international law, principles can be articulated that operationalize the abstract idea of shared responsibility and mitigate these negative consequences.