What is the theme in Bowling Alone by Robert D. Putnam?

One of the major themes in Bowling Alone is social capital. Putnam states that the term has been coined to refer to the way social bonds make people's lives more productive. This includes aspects such as fellowship, social interaction, sympathy, and social support. It has also been used to refer to social networks, which indicate that it is often who one knows and not what one knows when searching for a job or fulfilling other needs. Social capital for Putnam is both a private good and a public good, benefiting individuals, communities, and nations.