Ranks 50 of the largest cities on their volunteer rates, types of organizations through which residents serve, their main volunteering activities, the average hours per year, and volunteer rates for age and gender demographic groups. Analyzes social and demographic trends that affect city volunteer rates and finds the four key drivers of volunteering: community attachment, commuting times, high school graduation levels and poverty, and the prevalence of nonprofits and their capacity to retain volunteers from year to year.