The public service motivation literature has helped scholars and practitioners better understand who is attracted to public service and why. However, little is understood about how public service motivation in individuals may be cultivated or how it changes over time. This article uses panel data collected by the Corporation for National and Community Service to track the longitudinal effects of participation in the AmeriCorps national service program on participants’ public service motivation. Findings reveal that participation in AmeriCorps programs had positive effects on participants’ levels of commitment to the public interest and civic awareness immediately after the program; many of these program effects were sustained seven years later. However, when observed in isolation, the comparison group showed significant declines in levels of commitment to public interest and civic awareness over an eight-year period, suggesting that public service motivation may initially decline upon entry into a public service career.