In this entry, we survey key ideas about the construct of “the self,” tracing its development from evolutionary origins to contemporary theories in psychology and neuroscience. We highlight three organizing features of selfhood: reflexive consciousness, interpersonal relatedness, and agency. Drawing on work from philosophy and the cognitive sciences, we outline how the self has been conceptualized as both a product of mental processes and a participant in social life. We connect early philosophical theories, such as those proposed by Hume and James, to later psychological models that address the self-concept, motivation, regulation, and narrative identity. We also consider current challenges, including how digital environments and artificial intelligence are reshaping the way individuals construct identity, relate to others, and reflect on experience. These trends raise questions about how the self functions in technologically mediated contexts and how emerging tools might change scholarly understanding of personhood. We conclude by considering interdisciplinary approaches and future directions in research on the self.