 Different approaches to groups make different commitments with regard to the entities that should be included among the social groups—e.g., committees, teams, corporations, universities, nations, races, genders, red-haired people. Some theorists also propose that social groups must have certain distinctive characteristics, such as the members being in certain cognitive states or being subject to certain norms. Related to this is the question of whether there are distinct types of groups. Ritchie (2015) argues that there are two prominent types—organized groups, which are realizations of structured sets of nodes that stand in a functional relation to one another, and feature groups, which are collections of people who have a property or feature in common with one another. Thomasson (forthcoming) argues that an important way of characterizing groups is in terms of the norms they bear. Epstein (forthcoming) challenges simple typologies of groups and proposes a framework for the metaphysics of groups involving multiple dimensions.