City governments were an important source of environmental protection in the United States from the 1800s until well into the 1900s. However, since Congress passed a series of landmark environmental statutes in the 1970s, scholars have primarily equated environmental law with federal law. To the extent that scholars consider subnational sources of environmental law, they typically focus on states, rather than cities. This article shines a light on the role of cities in contemporary environmental law. It argues that major U.S. cities are currently reviving cities' historical role as leaders in environmental lawmaking and proposes mechanisms for expanding their scope to innovate within the framework that the 1970s federal environmental statutes established. The article makes three significant contributions to existing literature. First, it resurrects the little-known history of early municipal efforts to protect their environments, which illustrates cities' long-standing interest in environmental matters. Second, the article incorporates an original survey of environmental policies that cities have developed in recent years, which demonstrates the breadth of largely overlooked lawmaking. Third, the article offers a framework for conceptualizing the interplay between federal, state, and local laws and suggests strategies for finding greater space for municipal policy experimentation within cities' jurisdictional authority.