Marine protected areas (MPAs) provide both conservation and economic benefits. Recent international conservation actors have called for a dramatic increase in the area of MPAs from almost 8% to 30% of marine area by 2030 in a policy called 30X30. Both the economics and conservation science literature consider MPA decisions and MPA impact, although the economics literature focuses on fishery economic outcomes. This review uses an optimization framework for MPA decisions as a lens through which to evaluate the economics literature on MPAs in the context of the 30X30 expansion decisions. We argue for more economic analysis of MPA policy questions, including those around siting, design, restrictions, and management choices; impact evaluation; responses of people; low-income country settings and incomplete enforcement; spatial settings without metapopulations; and conservation rather than harvest objectives.