After exploring the challenges involved in defining incivility, this chapter addresses the evolution of the concept, notes the dispute over trend lines, and précises work on its psychological effects. It then outlines some functions that civility and incivility serve, such as the functions of differentiating and mobilizing, marginalizing the powerless, expressing, and deliberating. The use of calls for civility as a means of social control is discussed, and then the chapter flags questions worthy of additional attention.