This chapter reviews social capital as discussed in the literature, identifies controversies and debates, considers some critical issues, and provides conceptual and research strategies for building a theory. It argues that such a theory and the research enterprise must be based on the fundamental understanding that social capital is captured from embedded resources in social networks. Such measurements can strength of tie network bridge, or intimacy, intensity, interaction and reciprocity be made relative to two frameworks: network resources and contact resources. There are many other measures, such as size, density, cohesion, and closeness of social networks which are candidates as measures for social capital. Network locations are necessary conditions of embedded resources. By considering social capital as assets in networks, the chapter discusses some issues in conceptualization, measurement, and causal mechanism. A proposed model identifies the exogenous factors leading to the acquisition (or the lack) of social capital as well as the expected returns of social capital.