Despite its positive impact on students' understanding of the nature of science and science content knowledge, few secondary science teachers incorporate the history of science into their instruction. This article describes the effects of an online history of science course on preservice teachers' perceptions of and content and pedagogical knowledge for history of science-integrated science instruction. Eleven secondary preservice science teachers participated in a semester-long history of science course focused on developing their conceptual understanding of and pedagogical knowledge for incorporating history of science into their science instruction. Data were collected from preservice teachers' discussions, reflections, assignments, and surveys. Results indicate that participation in the online history of science course led to preservice teachers' understanding of history of science content and pedagogy and to positive perceptions about history of science-integrated science instruction. Preservice teachers also demonstrated skills for developing history of science instructional materials using "recurrent, storyline, and argumentation" approaches. Implications of the findings for secondary science teacher preparation are discussed.