Editors' Summary: The principles of federalism, state primacy, and tribal sovereignty all impact how federal environmental regulations are implemented and enforced on Indian lands. In recent years, Congress increasingly has crafted environmental protection laws that expressly provide recognized tribes with mechanisms for assuming authority to operate programs under those statutes, similar to provisions for states to obtain such authority. Yet many important federal environmental laws leave uncertain the role of Indian tribes in enforcing federal regulations on Indian lands. The courts, thus, have been left with the task of determining whether tribes may nonetheless receive authority to operate programs established by these laws under other, usually "inherent authority" or treaty-based, theories. The author reviews the environmental laws and regulations, and EPA's policies on treating tribes as states for purposes of assuming program authority. The author describes the federal statutes that expressly authorize EPA to treat tribes as states, including the Clean Water Act, the SDWA, the Clean Air Act, and CERCLA. He next discusses EPA's implementation of regulations to effect this authority, including tribal requirements, the effects of being approved for treatment as a state, EPA's attempt to simplify the process of approval, and the Agency's CERCLA regulations. The author analyzes federal environmental laws that do not expressly authorize treating tribes as states, including RCRA, FIFRA, TSCA, EPCRA, and the Pollution Prevention Act. He then discusses the key legal issues surrounding treating tribes as states, including jurisdiction over programs through inherent, or aboriginal tribal authority, and through delegated authority from Congress. The author concludes with a discussion of EPA's Indian policy to encourage tribal self-determination, including tribal assumption of regulatory and program management on Indian lands.