The geologic storage (GS) of carbon dioxide (CO2) is emerging as an important tool for managing carbon. While this Journal recently published an excellent review of GS technology (Bruant, R. G.; Guswa, A. J.; Celia, M. A.; Peters, C. A. Environ. Sci. Technol. 2002, 36, 240A-245A), few studies have explored the regulatory environment for GS or have compared it with current underground injection experience. We review the risks and regulatory history of deep underground injection on the U.S. mainland and surrounding continental shelf. Our treatment is selective, focusing on the technical and regulatory aspects that are most likely to be important in assessing and managing the risks of GS. We also describe current underground injection activities and explore how these are now regulated.