This article examines the critical didactic incidents (CDIs) method used by European researchers in didactics. Originally designed by Flanagan (1954) in psychology, the CDIs method is based on qualitative accounts and analysis of critical moments in the teaching process when content is brought into play. The article reviews the use of critical incidents in educational research and then focuses on the epistemological aspect of its recasting in didactics. Criteria and guidelines for using the method are described, as well as some tenets for interpretation. The description emphasizes the fact that the CDIs method is anchored in a concern for developing depth of understanding of a particular phenomenon: the dynamics of the implicit negotiations between teacher and students regarding content issues and the co-construction of meanings that undergirds classroom interactions.