Federal public lands are a major source for fossil fuel extraction in the United States—extraction that contributes to greenhouse gas emissions. Extraction occurs through the leasing of federal lands to private companies for development. Activists have called for ending new fossil fuel leasing as part of a “Keep It in the Ground” movement. We analyze the legal possibilities for more radical action—the termination of existing fossil fuel leases. We identify the possibility for both congressional action to terminate leases, as well as executive power to terminate leases even without additional legislation. We find strong legal arguments for executive power to breach these leases, albeit with the possibility that compensation to leaseholders might be required. We find it unlikely that courts would order specific performance by the federal government as a remedy for any breach; remedies would likely be limited to monetary damages. We conclude with a brief analysis of the policy consequences of terminating existing leases—such an approach would be an aggressive version of supply-side efforts to address greenhouse gas emissions, and its utility will vary depending on the fossil fuel.