Social capital "refers to the collective value of all 'social networks' and the inclinations that arise from these networks to do things for each other," according to Robert Putnam, author of Bowling Alone and the concept's leading exponent (though not its originator). According to Putnam and his followers, social capital is a key component to building and maintaining democracy.
The term "capital" is used by analogy with other forms of economic capital, as social capital is argued to have similar (although less measurable) benefits, and as a result is now considered by institutions such as the World Bank in deciding policy. Social capital is also argued to have a host of other benefits for societies, governments, individuals, and communities; Putnam likes to note that joining an organization cuts in half an individual's chance of dying within the next year.
However, social capital may not always be beneficial. Horizontal networks of individual citizens and groups that enhance community productivity and cohesion are said to be positive social capital assets whereas self-serving exclusive gangs and hierarchical patronage systems that operate at cross purposes to communitarian interests can be thought of as negative social capital burdens on society.
The concept of social capital in a Chinese social context has been closely linked with the concept of guanxi.
Nan Lin's concept of Social Capital has a more individualistic approach: Investment in social relations with expected returns in the marketplace. It may subsume some others concepts such as Bourdieu, Coleman, Flap, Putnam and Eriksson as noted in Nan Lin book �Social Capital� (2001) Cambridge University Press