Behavior is a reflection of the intentions, attitudes, goals, beliefs, and desires of a person. These intra-individual factors are coordinated with what opportunities the situation affords and the perceived constraints placed on the person by their context and the norms of the culture they are in. Further, the intentions, attitudes, goals, beliefs, and desires of a person are often not known to them in any given moment, and because they reside within the mind of that person they are almost always not known to the people who are perceiving that person. To know anything about other people we must observe and identify/classify their behavior and then attribute to the observed behavior inferences and judgments about the internal states of that person serving as the motivating force behind their behavior. This entry explores this process of attribution. Heider described attribution as the process that determines “how one person thinks and feels about another person, how he perceives him and what he does to him, what he expects him to do or think, how he reacts to the actions of the other.” The entry explores the rules that people follow in order to make sense of behavior, and the rational versus non-rational nature of the procedure. Even when highly motivated to think rationally, this process can be biased, and flaws can appear in the attribution process, such as from chronic differences among perceivers due to culture, experience, or personality. How the process would unfold if accurate and purely rational is contrasted with how it unfolds when biased. How we feel, and how we choose to act, are derived from how we make sense of the world. Thus, attribution processes are foundational for understanding how we feel, for establishing expectations, and planning how to act in turn.