Proof-based mathematics courses are often taught in a lecture-based format that deprives students of the opportunity to engage in authentic mathematical activity. Students are presented with mysterious answers to questions they have never even been asked to consider. Inquiry-oriented instruction (IOI) provides an alternative approach in which teachers engage students in deep mathematical sense-making as they inquire into both the mathematics and one another’s thinking. As part of a larger project, we have designed an inquiry-oriented instructional sequence that engages students in the reinvention of several real analysis concepts. In this chapter, we explore the mathematical activity of both the students and instructors in one course using this instructional sequence. Our results suggest that the principles of inquiry-oriented instruction provide important support for instructors who are motivated to provide students with an opportunity to engage in legitimate mathematical activity while also meeting expectations for content coverage.