The author, a professor of public policy at Harvard, gathers together dozens of studies that measure social engagement and involvement in various ways -- from voting and running for office to giving blood, having friends over for dinner, and doing volunteer work -- in order to chart the steady decline of what he calls "social capital" in the U.S. since it peaked in the early 1960s. Why do Americans give less to charity, play cards less often, fail to exercise their right to vote, and in so many ways fail to engage with the community and nation around them as much as they used to? Putnam charts the problem that so many of us have sensed vaguely but could not clearly identify, but has less to say about why it happened and what's to be done about it.