Theatrical improvisation is a joyful, creative, and playful activity of discovery and a spontaneous process. It seems to be the opposite of teaching, which requires proper planning and advance thinking and seems a very "serious business" that deals with values and knowledge. Improvisation is shaped by flexibility and by transformative and equal relations among the participants. In this article, the author tries to describe improvisation as a practical device and mode of knowing for improving teaching. First, he conceptualizes his theoretical framework, which is based on the concepts of aesthetic and theatrical knowledge and theatrical events. Second, he elaborates on theatrical improvisation and its principles. In the last part of this article, he presents the case of a student who taught a movement and drama lesson using, in her teaching, principles of improvisation to manage unexpected situations that took place in the classroom. (Contains 21 notes.)