This chapter describes a course in open scientific inquiry for preservice teachers. The course uses neither a textbook nor a lab manual, but instead engages students in developing models of puzzling phenomena through an iterative process of designing experiments, crafting models, debating, and refining ideas. We outline strategies for planning such a course, including materials and classroom setup. We discuss basic structures in the class, including introducing an initial question or phenomenon, engaging in small-group investigations, leading whole-class conversations, and assessing students’ work. Included are a range of examples of student ideas and student work, and results of surveys on students’ progress.