The grassroots movement that placed environmental justice issues on the national stage around 1980 was soon followed up by research documenting the correlation between pollution and race and poverty. This work has established inequitable exposure to nuisances as a stylized fact of social science. In this paper, we review the environmental justice literature, especially where it intersects with work by economists. First we consider the literature documenting evidence of disproportionate exposure. We particularly consider the implications of modeling choices about spatial relationships between polluters and residents, and about conditioning variables. Next, we evaluate the theory and evidence for four possible mechanisms that may lie behind the patterns seen: disproportionate siting on the firm side, “coming to the nuisance” on the household side, market-like coordination of the two, and discriminatory politics and/or enforcement. We argue that further research is needed to understand how much weight to give each mechanism. Finally, we discuss some policy options.