The word norm derives from the Latin norma, which referred to a square used by carpenters to obtain a right angle. The carpenter’s square is a fitting metaphor for what social scientists and philosophers usually mean by norm: A standard by which actions are evaluated, for instance as good, mandatory, permissible, bad, or wrong. The prohibition against killing, requirements for using proper titles (e.g., referring to people with an MD as Doctor), and speed limits on highways are all norms in this sense. Beyond this broad definition, scholars have differing theories about how norms are represented and used by adults, and these theories in turn inform research on how norms develop across the life span. This entry focuses on four key questions: (a) Are there ...