There is large variation across countries regarding their use of marine protected areas (MPAs) for conservation or sustainable management purposes. This is the first in-depth econometric analysis that makes use of a large panel dataset to identify the key socio-economic and geographical factors that correlate strongly with the extent of MPA coverage. The findings provide strong evidence of an Environmental Kuznets Curve in the domain of MPAs ? i.e. MPA coverage (as a share of total territorial waters) initially declines as average income per capita rises, but then starts increasing above a relatively low threshold level of economic development. This also holds when using the Human Development Index of the United Nations Development Programme in place of the level of (real) GDP per capita. There is also consistent evidence suggesting that democracy and population density are strong (positive and negative respectively) correlates of MPA coverage.