This chapter examines the role that the unconscious might play in creativity, focusing on the question of how the unconscious might work. The idea that unconscious processes are important in creativity raises questions for the analytic view. Taking a historical perspective, the chapter begins with Poincaré’s (1913) seminal theory of how unconscious thinking functions in creativity and traces the development of modern views, many of which have built on Poincaré’s ideas. This will lead us to recent research concerning the possible role of the unconscious in creative thinking, focusing on the study of incubation in problem-solving. This chapter deals with a very difficult question: how can one gather evidence concerning the unconscious, which is, by definition, not observable?