An influential research program in social science posits that personal networks are an important means to improve one's life chances next to human, economic, and cultural capital. This research line starts from the assumption that social networks can be instrumental to goal achievement and that a person's social network can therefore be conceived as that person's social capital. Thus, first, actors with more social capital will be better able to achieve their goals. Second, actors will invest in relationships to others to the extent that they expect that these relationships will be instrumental in the future. Social capital is located in people's structural 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. During the review period, studies have been undertaken in both problem areas, returns on and investments in social capital. For example, on how people get a better job or perform better in their job, but also on how physical and social order in a neighborhood depends on network structures in the neighborhood and on people's investments in these network structures. Furthermore, it has been studied to what extent returns on social capital depend on institutional contexts. A major development within the research line has been a growing emphasis on ‘supply side' explanations, e.g., what are the effects of meeting opportunities provided by various social contexts on the resulting networks? A recent shift has been the rise of a communitarian view on social capital, emphasizing the beneficial effects of trust in relative strangers. In addition, there is an upcoming interest in the dark side of social capital, e.g., what do enemies do to your life chances? For the upcoming years, more work can be expected on such ‘sour' social capital as well as on collective social capital. Moreover, work on a new generation of empirical studies on social capital is foreseen, i.e., international comparative studies as well as national longitudinal studies.

The coherence of the research line is provided by the key idea on social capital that informs on effects of social networks as well as on how networks are formed. Its originality largely comes from the parallel with human capital and the hypotheses this suggests on the importance of the expected value of future help or on institutional contingencies. Its importance is demonstrated in many research domains in which effects of social networks have been established.

The research line was initiated by Flap, later joined by Völker. Until 2004, the research line benefited from an NWO Integrated Research Program (‘aandachtsgebied') Creation and Returns of Social Capital. Social Networks in Education and Labour Markets with Flap as principal investigator. Major new research grants during the review period have been secured by Völker, namely, a KNAW-fellowship, an NWO VIDI grant Where Friends Are Made. Contexts, Contacts, and Consequences, and (with Schutjens, UU Social Geography) a UU High Potential program Life Chances of Firms and Neighborhoods. A major result of these grants is the panel study Survey of the Social Networks of the Dutch (SSND) on the networks of the Dutch. Representative publications during the review period are the edited volume Creation and Returns of Social Capital. A New Research Program by Flap & Völker (Routledge 2004), an article by Kalmijn & Flap (2001) in Social Forces, and an article by Völker & Flap (2001) in Rationality and Society.