This study investigates trends in social capital in the United States since the 1970s. The literature suggests that variations in social capital are associated with both individual attributes and macro-level economic conditions. Yet, others argue that after controlling for these features, large-scale changes in social capital are evident across birth cohorts and over time. While previous studies have identified a number of individual and societal factors that influence social capital, I note that the common modeling approach used is inappropriate for examining the interaction between national and individual-level data as well as the simultaneous influence of period- and cohort-based effects. I therefore utilize a multilevel model to reassess the different theories of the origins and determinants of social capital. The evidence presented casts doubt on past studies that see a general erosion in social capital as well as those that view the decline as stemming from generational replacement.