Abstract
This chapter characterizes social groups and institutions in a way that meets the plausible objections of individualists, yet allows a social explanation of oppression. Topics discussed include explaining human behavior, social groups, institutionally structured constraints, oppression and social groups, social groups and group harm. It is argued that any account of oppression that distinguishes it from other types of harm that can come to individuals and locates it as a social injustice requires an account of social groups. Further, harms that accrue to members of voluntary and nonvoluntary groups must be treated separately in moral arguments.