What are groups? A group is any assortment of people who share norms, values, and expectations. They can be large or small, formal or informal. Our group memberships are among the defining features of...

What are groups? A group is any assortment of people who share norms, values, and expectations. They can be large or small, formal or informal. Our group memberships are among the defining features of our lives, both for our definitions of self and others’ ideas of who we are. Groups are primary, coming together for expressive reasons, or secondary, coming together for instrumental reasons. We also see groups in terms of in-groups, to which we belong, and out-groups, to which we do not belong. In-group–out-group rivalry can lead to dire consequences.