Cross-sector collaborations – defined as collective initiatives involving joint work between any combination of public, not-for-profit, and for-profit actors – are increasingly viewed as valuable to foster social innovation and address some of the world’s most pressing societal challenges. However, they are also recognized to be particularly challenging to implement. This chapter reviews the academic literature on cross-sector collaborations produced in the past two decades to understand what makes these collaborations work and identifies three main organizational-level determinants of their success: the characteristics of the partners involved, the structure of the collaboration, and the boundary practices that are used by those that collaborate. We detail each of these determinants and further leverage general knowledge on collaboration to show how they contribute to the two main mechanisms facilitating collaboration, namely cooperation and coordination. Building upon this review, we discuss the limitations and gaps in the existing literature and point to potential future research directions.