In the decades since Congress and state legislatures passed most of the nation's most significant environmental laws, our knowledge about ecosystems has increased dramatically. As ecologists learn more about the complex and dynamic interactions that produce valuable ecosystem services, decisionmakers and advocates should adopt an ecosystem services approach to implementing laws that affect the environment. An ecosystem services approach integrates advances in ecology with the law. It fosters creative thinking about how to restructure laws and regulatory programs to mimic the connectedness of ecosystem functions. The approach requires performance-based evaluations to measure success or failure of management decisions, and it depends on public participation to prioritize those services that the public values most, thus ensuring long-term public support for and investment in achieving the identified goals. This white paper defines the approach and identifies both prerequisites and principles for implementing it. For example, policymakers and advocates should consider principles of ecological integrity, fairness, and resilience when selecting legal tools to protect ecosystem services. The paper then applies the ecosystem services approach in the context of floodplain restoration, focusing on flood hazard mitigation and the broad range of services provided by floodplains. It marks the beginning of a long-term discussion on how to adapt environmental, natural resources, and other laws to our dependence on functioning, dynamic ecosystems.