There is a long history of philosophical inquiry into the concept of explanation in science, and this work has some implications for the ways in which science teachers, particularly in the physical sciences (physics and chemistry), explain ideas to students. Recent work has outlined a constructivist approach to developing, delivering, and refining explanations focused on enhancing student's understanding of the powerful concepts of science. This paper reviews the history of concepts of explanation in science and in science teaching, and reports research findings that describe some ways in which science teachers have been observed to explain ideas in Year 11 Physics classrooms in Australia and Canada.