This paper contributes to a growing body of research on the study of classroom learning and instruction in specific subject matter areas. It addresses the broad issue of the nature of and occasions for instructional explanations in history. Based on a study that traced the classroom instruction of one exemplary US history teacher for an entire semester, the paper presents a typology of instructional explanations in this discipline. Analysis of the lessons shows how the teacher uses each type of instructional explanation and how students acquire competence in constructing their own explanations as the year progresses.