This paper presents the results of an inductive, interpretive analysis of the perspectives of 42 Canadian high school distance education (DE) teachers on asynchronous and synchronous online teaching. The paper includes a conceptual overview of the affordances and constraints of each form of teaching. Findings provided insight into the following aspects of asynchronous and synchronous online teaching: degree of use; the tools used; the contexts in which each occur; students' preferences; and limitations. Pedagogy emerged as more important than media for both asynchronous and synchronous online teaching. Synchronous online teaching relied on teacher- rather than student-centred approaches. Asynchronous online teaching provided support for self-paced, highly independent forms of secondary DE supplemented by synchronous online teaching for answering questions and troubleshooting.