This chapter discusses the role of argumentation in promoting change in the epistemic status of ideas during conceptual change. We examine conceptual change in two contexts: (a) modification of models and explanations, or conceptual change in the strict sense; and (b) changes in decisions about scientific dilemmas of social relevance, involving modification of positions or beliefs, but also making sense of concepts. Conceptual change requires modification of the epistemic status of learners’ ideas, with some differences in both contexts, involving changes in: (a) the plausibility and explanatory power of models; or (b) the degree of acceptability of options.