Insight is a sudden realization of the gist of a problem. The notion was introduced by Gestalt psychologists in opposition to the trial-and-error model of problem solving. This article describes three typical features of insight, that is, the experience of suddenness, the incubational break, and the change of configuration of the problem's elements (restructuring). Relevant empirical data are provided to illustrate these features. Then, three theoretical models of insight are discussed: selectivity of cognitive processes, simplification of the problem structure, and assimilation of external cues. These models have been formulated in order to account for the typical features of the phenomenon of insight.