In an effort to more comprehensively understand economics as a foundation of human resource development (HRD), this article reviews economic theories and models pertinent to HRD research and theory building. By examining neoclassical and neoinstitutional schools of contemporary economics, especially the screening model and the internal labor market theory, it is argued that economic theories not only provide a foundation but also have important implications to HRD theory, research, and practice. Broadening research directions may be fruitful and provocative in expanding HRD's theoretical base as well as practical applications in organizations. (Contains 1 table and 1 note.)