Cooperative federalism can lead to more efficient and pragmatic environmental protection, and allow states to develop effective programs tailored to their needs and resources. Nevertheless, the future of the federal-state relationship in the environmental context is uncertain as state and federal priorities come into conflict: for instance, EPA’s proposal to revoke California’s authority to regulate tailpipe emissions of greenhouse gases. Recent reports have begun a discussion on the future of cooperative federalism and environmental protection, but significant questions remain unanswered. On February 28, 2019, ELI held a discussion of the opportunities presented by increased state autonomy in environmental protection, including panelists expert in interstate environmental coordination and with significant experience in environmental compliance and stewardship. This Dialogue presents a transcript of the discussion, which has been edited for style, clarity, and space considerations.