This article addresses the purposes and types of opportunities for engaging students in argumentation in the mathematics classroom. Drawing on data from a research project, we document how argumentation--a practice that is central to the work of the mathematics community--can be contextualized in secondary mathematics classrooms to serve different purposes. We focus on 2 complementary purposes--argumentation for concept development and argumentation for mathematical practice development. We explore how the nature of opportunities provided for students to engage in argumentation may reflect different valued purposes of argumentation, ultimately shaping students' understanding of the practice of mathematical argumentation. We conclude with a discussion of tensions and recommendations related to offering students a robust view of this crucial practice.