Why do some governments implement more sustainability practices than others? Based on a national survey of U.S. cities, this article finds moderate levels of sustainability efforts and capacity in U.S. cities; about one-third of the sustainability practices identified in this article have been implemented. The authors conclude that, first, capacity building is a useful conceptual focus for understanding sustainability implementation in U.S. cities. Capacity building involves developing technical and financial support and increasing managerial execution. Second, sustainability is strongly associated with managerial capacity, which includes establishing sustainability goals, incorporating goals in operations, and developing a supportive infrastructure. Third, getting stakeholders involved furthers the capacity for sustaining sustainability efforts. Citizen involvement is strongly associated with securing financial support for sustainability.