Purpose: The purpose of this study was to explore the foundational theories in human resource development (HRD) by reviewing the literature from an HRD perspective. The following research questions guide the study: What are the core theories related to adult and professional education, organizational development and strategic HRD? What are the conceptual frameworks associated with adult and professional education, organizational development and strategic HRD? How have these theories and conceptual frameworks applied the research and practice of HRD? Design/methodology/approach: This study reviewed the HRD definitions and core theories. The core theories and conceptual frameworks related to adult and professional education, organizational development and strategic human resource development were described. The application of these theories and conceptual frameworks to the research and practice of HRD was addressed. Findings: The psychology theories that were explored were the adult learning theories, and that gestalt-psychology, behavioral psychology and cognitive psychology were illustrated. Systems theory was explored and explained in relation to organization development. Economic theory was explored and explained focusing on human capital theory; and it was demonstrated how economic theory is associated with strategic HRD. Originality/value: The core-theory description and linking to adult and professional education, organizational development and strategic HRD may give understanding of the HRD foundations and ethical perspective that is essential for both scholars and professionals. The conceptual frameworks presented can be used to help facilitate discussions on developing or implementing HRD programs.