This paper examines the relationship between positive and normative economic theories of discrimination, that is, what discrimination is and why law should prohibit it. Prior economic scholarship has modelled discrimination as the result of (a) a taste for non-association; (b) statistically rational generalizations; and (c) group-based status competition. I examine these theories along with the psychological theory of implicit bias and other types of irrational stereotypes. For each positive theory, I explore the normative implications. The taste-based and statistical theories do not match well with antidiscrimination law, though the status theory potentially does.