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. We know much more about the “goods and services” that ecosystems provide—more, for example, about the migratory species that sustain agriculture by functioning as pollinators, and more about how healthy ecosystems help to filter and clean our water. But our policymakers haven’t yet taken advantage of much of that new knowledge. As ecologists learn more about the complex and dynamic interactions that produce these valuable services, decisionmakers and advocates should adopt an ecosystem services approach to implementing laws that affect the environment. A recent CPR publication, Letting Nature Work in the Pacific Northwest: A Manual for Protecting Ecosystem Services Under Existing Law, defines the ecosystem services 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 publication 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 offers recommendations on how the Clean Water Act, the public trust doctrine, and the National Flood Insurance Program can be used to promote ecological integrity and protect the ecosystem services that we value. This publication 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. This paper defines the ecosystem services 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 publication 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 offers recommendations on how the Clean Water Act, the public trust doctrine, and the National Flood Insurance Program can be used to promote ecological integrity and protect the ecosystem services that we value. This publication 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.