Bowling Alone, written by Harvard political science professor Robert D. Putnam, is a study of the decline in social capital among Americans. Written in 2000, the book chronicles the collapse of social ties that unite Americans in the past several decades and examines the reasons for this decline.

Putnam's study relies on a wealth of data. He looks at the ways in which Americans' participation in different areas of life has declined in several areas, including political and civic participation. He likens his approach to studying the decline of social connections to the study of global warming. He writes that measuring the decline of social capital requires the triangulation of data, just as paleontologists measure different kinds of data, including temperature records and the pollen levels in polar ice, to substantiate the fact of global warming. After triangulating the data from many sources, Putnam finds that social connections among Americans have declined, and he then tries to figure out the reasons why. After discounting several explanations, including the idea that Americans are working more, he explains that most of the decline can be attributed to the rise of television and the internet.

Putnam uses several motifs to explain the importance of social capital. He refers to social capital as a "WD-40." It is the glue that keeps the society together, and it is important for this reason, as it establishes a sense of reciprocity among different people. The motif of bowling alone occurs often in the book. The idea behind this motif is that people are not bowling in organized leagues anymore, which used to be a form of social connection. Instead, Americans are increasingly turning to informal groups or to solitary pursuits that do not connect them to others. Putnam posits that the lack of social and other connections among Americans is troubling and wonders how Americans might change so that society can be more closely knit together.