Glossary

Separation of powers

The constitutional division of government into legislative, executive and judicial branches, each with its own distinct powers.

Also called: separation of powers doctrine, tripartite government

Separation of powers is the structural principle that government power should be divided among distinct branches so that no single person or body controls all of it. The U.S. Constitution vests legislative power in Congress (Article I), executive power in the president (Article II) and judicial power in the courts (Article III).

The idea draws on Montesquieu and was defended by James Madison in The Federalist, especially No. 47 and No. 51, which argued that accumulating all powers in the same hands is the very definition of tyranny. The branches are not sealed off from one another; the framers deliberately overlapped them through checks and balances such as the veto and Senate confirmation.

Separation of powers drives many current legal fights: whether Congress can delegate lawmaking to agencies under the nondelegation doctrine, whether presidents can fire officials at independent agencies, how far executive orders reach and when courts should intervene. Conservatives often invoke it against the growth of the administrative state; supporters of the unitary executive theory invoke it for presidential control of the executive branch; critics of strong presidencies invoke it to defend Congress's role.

Last reviewed November 8, 2026

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Related terms

Checks and balances The constitutional design giving each branch of government ways to limit the others, so that no branch dominates. Nondelegation doctrine The principle that Congress may not hand its lawmaking power to agencies or others without clear limits on how it is used. Unitary executive theory The theory that Article II gives the president full control over the executive branch, including the power to direct and remove its officers. The Federalist Papers A series of 85 essays from 1787-1788 by Hamilton, Madison and Jay urging ratification of the Constitution. Judicial review The power of courts to strike down laws and government actions that conflict with the Constitution.