The blue hat, its color chosen for its association with the sky, is for “thinking about thinking” (145). Used at the beginning of a thinking session, it defines the situation, lays out its purpose, and specifies the agenda or sequence of use of the other hats. The hat is typically worn by the facilitator, chair, or leader of the session, who also announces when it is time to change hats.

As the session ends, the blue hat asks for the outcome. This could be a summary, conclusion, decision, or solution.

When wearing the blue hat, people do not think about the subject but instead about the thinking needed to explore the subject. De Bono compares the blue hat to a computer program that tells the machine what to do from moment to moment. The blue hat is the “programming hat for human thinking” (147). It structures a thinking session formally and can also be used to give moment-to-moment instructions, for instance by saying a group should begin looking for alternatives.

De Bono revisits his metaphor of map-making for the parallel thinking process, in which the “terrain” is first explored, then routes are observed, and finally a route is chosen.