Once we bowled in leagues, usually after work; but no longer. This seemingly small phenomenon symbolizes a significant social change that Robert Putnam has identified and describes in this brilliant volume, "Bowling Alone." Drawing on vast new data from the Roper Social and Political Trends and the DDB Needham Life Style -- surveys that report in detail on Americans' changing behavior over the past twenty-five years -- Putnam shows how we have become increasingly disconnected from family, friends, neighbors, and social structures, whether the PTA, church, recreation clubs, political parties, or bowling leagues. Our shrinking access to the "social capital" that is the reward of communal activity and community sharing is a serious threat to our civic and personal health. Putnam's groundbreaking work shows how social bonds are the most powerful predictor of life satisfaction. For example, he reports that getting married is the equivalent of quadrupling your income and attending a club meeting regularly is the equivalent of doubling your income. The loss of social capital is felt in critical ways: Communities with less social capital have lower educational performance and more teen pregnancy, child suicide, low birth weight, and prenatal mortality. Social capital is also a strong predictor of crime rates and other measures of neighborhood quality of life, as it is of our health: In quantitative terms, if you both smoke and belong to no groups, it's a close call as to which is the riskier behavior. A hundred years ago, at the turn of the last century, America's stock of social capital was at an ebb, reduced by urbanization, industrialization, and vast immigration thatuprooted Americans from their friends, social institutions, and families, a situation similar to today's. Faced with this challenge, the country righted itself. Within a few decades, a range of organizations was created, from the Red Cross, Boy Scouts, and YWCA to Hadassah and the Knights of Columbus and the Urban League. With these and many more cooperative societies we rebuilt our social capital. We can learn from the experience of those decades, Putnam writes, as we work to rebuild our eroded social capital. It won't happen without the concerted creativity and energy of Americans nationwide. Like defining works from the past that have endured -- such as "The Lonely Crowd" and "The Affluent Society" -- and like C. Wright Mills, Richard Hofstadter, Betty Friedan, David Riesman, Jane Jacobs, Rachel Carson, and Theodore Roszak, Putnam has identified a central crisis at the heart of our society and suggests what we can do.