Network research is booming. This creates the need for theoretical integration. Structuralism was a powerful attempt to provide such an integration, but it failed to fill the theory-gap. In this contribution the research program of social capital theory is discussed. This program assumes that personal networks are an important means to im-prove one"s life chances next to human, economic, and cultural capital. This research line starts from the assumption that social networks can be instru-mental to goal achievement and that a person"s social network can therefore be conceived as that person"s social capital. Actors with more social capital will be better able to achieve their goals. Further, actors will invest in rela-tionships to others to the extent that they expect that these relationships will be instrumental in the future. Social capital is located in people"s struc-tural embeddedness in networks, but also in the resources their ties provide access to. Returns on and investments in social capital thus affect cohesion and solidarity and are connected to problems of inequality. Main charac-teristics of this program are discussed as well as its relative success in inte-grating network research.