The Sage Handbook of Theoretical Psychology is a comprehensive resource that explores the foundational and evolving theories within the field of psychology. This handbook emerged from a conversation between the editors, recognizing the absence of a dedicated handbook on psychological theory that covered the wide range of theories. It addresses the implicit role of theory in all aspects of psychology, often overshadowed by the dominant emphasis on empiricism. The handbook begins with foundational questions central to contemporary psychology, including chapters on cognitive representations, evolutionary theory, the extended mind thesis, mental causation, feminist psychology and cultural psychology. Each chapter provides an in-depth exploration of these topics, updated to reflect the latest developments and debates in the field. Contributors to this volume come from diverse disciplinary backgrounds and nationalities, ensuring a rich and multifaceted perspective on psychological theory. They tackle complex issues such as the definition and role of mental representations, the adaptation of evolutionary psychology to criticism, the integration of machine learning into cognitive repertoires, the implications of mental causation for moral responsibility and free will, and the necessity of a truly cultural psychology. The Sage Handbook of Theoretical Psychology is an essential resource for scholars, practitioners, and students seeking to deepen their understanding of psychological theory. It provides a comprehensive and nuanced exploration of the field, equipping readers to engage with the theoretical underpinnings of psychology and contribute to its ongoing development.