This chapter summarizes Piaget's theory of intelligence. We first show how Piaget's conception of intelligence builds on that of his contemporaries. Then we discuss how his conception of intelligence is contextualized within his larger theoretical framework, which leads us to a discussion of core features of Piaget's theoretical framework such as self-organization, assimilation and accommodation, and operative and figurative aspects of intelligence. Next, we summarize the four major stages of the development of intelligence. Finally, we describe how Piaget's theory of intelligence relates to semiotic function, affectivity, and social interaction.