A phenomenographic study at a research university identified five categories of description for how STEM (science, technology, engineering, and mathematics) instructors conceptualize the design and redesign of undergraduate courses. These categories form a hierarchical outcomes space with increasing complexity of awareness of the phenomenon. The basic conceptualization (Category 1) is individual focus on the content to teach. Another focus turns to how to teach the content (Category 2). In Category 3, course design involves critical reflection that informs adjusting what is taught and how it is taught. Category 4 extends course design from individuals to collaborative activity within a department. In Category 5, instructors' course-design lens expands beyond a department to embrace collective engagement with people across disciplines and universities to develop a culture to innovate teaching and learning. The study shows that instructors, administrators, and faculty developers should view course design not only as a variety of individual approaches, but also as opportunities to stimulate networks to enhance the design process and its impact.