This document summarizes attribution theory, which examines how people make sense of human behavior through attribution as explanation and attribution as inference. Attribution as explanation refers to how people answer "why" questions about behavior by selecting reasons for intentional acts or causes for unintentional acts. Attribution as inference refers to deducing unobservable properties like intentions or emotions from observable behavior. While related, explanations are also social and communicative acts used to construct meaning from behavior between individuals and within cultures.