This study examined influences upon experienced teachers' course planning. Seven teachers were each intensively interviewed four times about their planning for courses they had never before taught; the interviews took place before, after, and twice during the semester of the "new" course in question. Findings were classified into three categories of influences drawn both from others' research and from the interviews: the disciplinary, the educational, and the organizational contexts for course planning. Four interpretations resulted: the reaffirmed primacy of disciplinary considerations in course planning; the educational and organizational bases for change; the overriding importance of the course's organizational context; and the cyclic nature of course planning. The Contextual Filters model developed at the National Center for Research To Improve Postsecondary Teaching and Learning is described and expanded. Contains 21 references. (Author/GLR)