Marine Protected Areas (MPAs) are promoted as an important marine ecosystem management tool. However, they are complex systems that, from a governance perspective, raise serious challenges with regard to their effectiveness. In this paper, drawing on recent contributions to the so-called "interactive governance theory," we argue that marine and coastal governance is basically a relationship between two systems, a "governing system" and a "system-to-be-governed." The former system is social: it is made up of institutions and steering mechanisms. The latter system is partly natural, partly social: it consists of an ecosystem, and the resources that this harbours, as well as a system of users and stakeholders who, among themselves, form political coalitions and institutions. We need to be concerned with the relationship and the interaction between the governing system and the system-to-be governed, which forms a system in its own right. Governance theory argues that both systems and their interactions share similar attributes-they are diverse, complex, dynamic and vulnerable. This raises serious concerns as to their governability. There may be limits to what the governing system can do, limits attributed to one or all three systems. But such limits are themselves issues and concerns for planning and institutional design. In this paper we present, in the form of a governance matrix, the relevant issues and concerns with regard to the governability of MPAs.