The United States is a republic which operates under federalist system. The national government has specific, enumerated powers, and the fifty sovereign states retain substantial autonomy and authority over their respective citizens and residents. Both the national government and each state government are divided into executive, legislative, and judicial branches. Written constitutions, both federal and state, form a system of separated powers, checks, and balances among the branches.

Any powers not delegated to the federal government in the United States Constitution, nor prohibited by it to the states, are reserved to the states or to the people. Nonetheless, the powers of the federal government are extensive. The federal government's authority to regulate interstate makes it the predominant force in environmental regulation. The states, under their general police powers to protect the public health, safety and welfare, also retain substantial independent authority to issue environmental protection laws applicable to their citizens and residents.

Potential conflicts between state and federal regulation in all areas, including environmental protection, are governed by the Supremacy Clause of the United States Constitution. The federal Constitution, federal laws, and international treaties are supreme to state or local law; state and local laws that contradict federal laws or treaties are thus preempted and can be declared unconstitutional by a federal court.

Although the Constitution sets forth the basic framework for national and sub national relationships in the United States, many environmental statutes add detail to specific aspects of those relationships within the broader constitutional framework. For example, federal statutes might explicitly preempt, or explicitly waive any preemption of, state law. Some federal environmental statutes create national minimum standards delegating primary implementation of federal programs to states that meet certain federal standards. States are free to enact stricter regulations. Many federal environmental statutes also provide for grants, technical assistance and other support to assist the states in furthering national policies or programs.