The focus of this study was language teachers' practical knowledge with respect to the teaching of reading comprehension to 16 to 18-year-old students. Based on the assumption that teachers are professionals, an attempt was made to define their shared knowledge. However, the results revealed such a wide diversity in teachers' practical knowledge that, instead of defining the shared knowledge, a typology of practical knowledge had to be developed. Three types of practical knowledge (with respect to the teaching of reading comprehension) were found that focus on (a) subject matter knowledge, (b) student knowledge, and (c) knowledge of student learning and understanding. In this article these types are described and illustrated. Suggestions are made about the extent to which practical knowledge needs to be shared by teachers and about how it can contribute to the better preparation of beginning teachers.