The United States federal government is comprised of three branches: the executive branch, the legislative branch, and the judicial branch.

Executive Branch
The executive branch includes the President, the Vice President, the Cabinet and all federal departments, and most governmental agencies. All executive power of the government is vested in the President, who serves a four-year term. The President is the Commander in Chief of the military, and has primary authority over foreign affairs. The President has the power to make treaties, but only with the approval of two-thirds of the United States Senate. The President also has the power to nominate all Supreme Court Justices, all other federal judges, ambassadors, and all other officers of the United States. The President has the power to veto legislation. The Vice President is also the President of the Senate, but votes only in the case of a tie vote in the Senate. The Vice President serves the same four-year term as the President.

The President selects the heads of the 14 government departments. These departments are not specified in the Constitution and have varied in name and number over time. They now are the Department of State, Treasury, Defense, Justice, Interior, Agriculture, Commerce, Labor, Health and Human Services, Housing and Urban Development, Transportation, Energy, Education, and Veterans Affairs. The heads of the departments form the Cabinet, which is the highest advisory group to the President. The executive branch also includes dozens of governmental agencies. The primary difference between agencies and departments is that agencies serve a very specific need. Government agencies include, for example, the Environmental Protection Agency (EPA) and the Federal Trade Commission (FTC). The Administrator of the Environmental Protection Agency, the head of that agency, is not a member of the Cabinet.

Legislative Branch
All federal legislative powers are vested in the Congress of the United States, which consists of two chambers: a Senate and a House of Representatives. There are 100 Senators, two from each of the fifty states. Senators serve six-year terms. The House of Representatives has 435 members, which are apportioned by population, with each state guaranteed at least one Representative. Representatives serve two-year terms.

The powers of the Congress are specifically enumerated in the Constitution and include, among other things, the power to lay and collect taxes, duties, and tariffs. Congress also has the power to regulate commerce with foreign nations, among the several states, and with Indian tribes. This "Commerce Clause" provides the authority for most federal regulation of the environment.

To become law, a bill must be passed by both the House and the Senate, and signed by the President. The President has the option of vetoing the legislation, but the Congress can override the veto with a two-thirds vote of both chambers.

The Congress also has substantial powers in overseeing the activities of the executive branch. The House of Representatives has the sole power to impeach the President and other officers, and the Senate the sole power to try impeachment. United States Congressional committees may demand disclosure of information and require agency officials to testify before them. The Congress has also established the General Accounting Office (GAO), which evaluates executive branch activities and reports back to the Congress. Most GAO reports are public documents.

Much of Congress' work is done by Congressional committees. The number and scope of Congressional committees can change, particularly when political control of the chamber changes parties and when the jurisdiction of committees overlaps, as is often the case. In the Senate, the following committees currently have jurisdiction over issues relating to environmental protection or natural resource conservation: the Agriculture, Nutrition, and Forestry Committee; the Appropriations Committee; the Commerce, Science and Transportation Committee; the Energy and Natural Resources Committee; the Environment and Public Works Committee; and, the Governmental Affairs Committee. In the House of Representatives, the following committees have jurisdiction over environmental protection or natural resource conservation: the Agriculture Committee; the Appropriations Committee; the Commerce Committee; the Government Reform and Oversight Committee; the Resources Committee; the Transportation and Infrastructure Committee; and, the Science Committee.

Judicial Branch
The federal judiciary is hierarchical. The highest court in the United States, and the only one required by the Constitution, is the United States Supreme Court. The Supreme Court's decision is the final decision in any case. The Supreme Court has nine members: a Chief Justice and eight Associate Justices. The Supreme Court has limited original jurisdiction, hearing most of its cases on appeal. In most cases, the losing party must petition the Court through a writ of certiorari to hear the case. The Court votes first on the writ, requiring four yes votes to hear the case.

The Circuit Courts of Appeals are the level of courts immediately below the Supreme Court. The Circuit Courts hear appeals from the District Courts, the lowest level of federal courts. There is one Federal Circuit Court, one D.C. Circuit Court, 11 other Circuit Courts, and more than 90 District Courts. The Congress has also established several courts that address special types of cases. Cases from these courts are appealed to the United States Court of Appeals for the Federal Circuit. These include the United States Court of Federal Claims, the United States Court of International Trade, the United States Court of Veterans Appeals, the International Trade Commission, the Board of Contract Appeals, the Patent and Trademark Office, and the Merit Systems Protection Board. Cases from the Court of Military Appeals are appealed directly to the Supreme Court.

All federal judges are appointed by the President and approved by the Senate. Federal judges hold their office for life, subject to impeachment by Congress. They have authority to interpret the Constitution, all federal statutes, treaties, and federal administrative rules, but their authority is limited to actual cases and controversies. The federal courts do not provide advisory opinions. The federal courts also have authority to naturalize persons as United States citizens and to settle certain legal disputes, such as: between citizens of different states; between two or more states; between individuals and the federal government; between states and the federal government; and, between states and foreign governments.