This handbook aims to show the importance of human capital (HC) for contemporary organizations: how it contributes to theories of the firm, how it affects organizational performance, and its role in the future economy. It identifies HC as the linchpin of social and other forms of capital. The article also shows how applying the notion of HC to organizations requires consideration of how human and other intangible intellectual forms of capital differ from more traditional forms, implying the need for a theory of the firm that accommodates a concept of dynamic, heterogeneous HC. It focuses on five aspects of HC: its conceptual underpinnings; its relevance to theories of the firm; its implications for organizational effectiveness; its interdependencies with other resources; and its role in the future economy.