This article reviews over 30 years of research on the role of integrative complexity (IC) in politics. IC is a measure of the cognitive structure underlying information processing and decision making in a specific situation and time of interest to the researcher or policymaker. As such, it is a state counterpart of conceptual complexity, the trait (transsituationally and transtemporally stable) component of cognitive structure. In the beginning (the first article using the measure was published in 1976), most of the studies were by the author or his students (or both), notably Philip Tetlock; more recently, IC has attracted the attention of a growing number of political and social psychologists. The article traces the theoretical development of IC; describes how the variable is scored in archival or contemporary materials (speeches, interviews, memoirs, etc.); discusses possible influences on IC, such as stress, ideology, and official role; and presents findings on how measures of IC can be used to forecast political decisions (e.g., deciding between war and peace). Research on the role of IC in individual success and failure in military and political leaders is also described.