This multiple-case study examined the rationales and instructional strategies for teaching history of science (HOS) of 16 instructors of a history of science course for undergraduate preservice teachers in the USA. Based on instructor syllabi, instructional materials, and instructor interviews, we conducted single-case and cross-case analyses to identify why they teach HOS (rationales), how they teach HOS (instructional strategies), and what possible relationships might underlie instructor rationales and their instructional strategy choices for teaching HOS. We found 10 rationales in three overarching categories (knowledge, skills, and attitudes) and 9 active-learning instructional strategies. Moreover, we found that instructors with skills rationales implemented active-learning instructional strategies, whereas instructors who only cited knowledge rationales relied only on lectures and reading discussions. We discuss implications and recommendations for the design of HOS courses.