Marine protected areas (MPAs) are currently receiving considerable attention as a "new" tool to control overexploitation. Many advocates argue that MPAs will provide a plethora of benefits ranging from improved habitat to higher fish stocks with little costs. Fishermen argue, not surprisingly, that the costs resulting from closing areas could be significant and need to be considered in the debate. In this paper, a set of biological, industry, and management hypotheses drawn from the literature analyzing the effects of MPAs are discussed. In doing so, a framework is presented that can be used to assess the expected returns to society from investing in MPAs.