On December 19th, 2023, the United States announced the outer limits of its continental shelf in areas beyond 200 nautical miles from the coast, known as the extended continental shelf (ECS). The U.S. ECS area is approximately one million square kilometers spread across seven regions and the United States has sovereign rights to conserve and manage the resources of the seabed and subsoil in this area. This was the culmination of a decades-long effort by multiple U.S. agencies — led by the Department of State, NOAA, and USGS — to map, analyze, determine, and document these limits, in accordance with provisions of Article 76 of the UN Convention on the Law of the Sea. We present some of the methodologies and results of work by CIRES scientists on the ECS Project, which led to roughly 2000 pages of documentation and more than 1000 maps and figures. We will also describe future work of the ECS Project Office, including Limits of the Seas studies, analyses on identifying potential marine protected areas in areas beyond national jurisdiction, and technical support to delineate maritime boundaries with neighboring countries.