This chapter discusses the course of development for deductive and inductive forms of reasoning across childhood and adolescence. Key theories of how best to account for that course are critiqued. The development of deduction is considered primarily with respect to syllogistic and conditional reasoning. Mental logic, metacognitive, and mental models accounts of deduction are contrasted and compared and the potential for rapprochement is identified. The development of inductive reasoning is discussed with respect to three primary types of induction—category‐based induction, causal induction, and inductive processes in scientific thinking. The discussion of the development of reasoning provided in this chapter is situated within a dual systems or dual process account of cognition. According to this account, human cognition consists of two distinct systems (1 and 2) or types of processing, with the primary basis for the distinction being the question of whether processing engages working memory resources. By adopting this framework, it becomes possible to shed light on the processes that underlie deductive and inductive reasoning and to trace how the development of each type of reasoning is related to changes in these underlying processes. Among the key conclusions of the chapter is that while the development of certain aspects of System 1 processing contributes to age‐related changes in performance on reasoning tasks, the most significant changes in both deductive and inductive reasoning result from key developments in System 2 processing.