Human capital is the stock of skills that the labor force possesses. The flow of these skills is forthcoming when the return to investment exceeds the cost (both direct and indirect). Returns to these skills are private in the sense that an individual’s productive capacity increases with more of them. But there are often externalities that increase the productive capacity of others when human capital is increased. This essay discusses these concepts historically and focuses on two major components of human capital: education and training, and health. The institutions that encourage human capital investment are discussed, as is the role of human capital in economic growth. The notion that the study of human capital is inherently historical is emphasized and defended.