The United States Congress is the legislative branch of the U.S. federal government, established as an institution by Article I of the U.S. Constitution. It is a bicameral legislature, meaning it consists of two chambers: the upper body, the Senate, and the lower body, the House of Representatives. The Congress was first organized on March 4, 1789, replacing the unicameral Congress of the Confederation. The new structure was created to solve the problem of a weak central government under the Articles of Confederation, which lacked the authority to collect taxes, regulate commerce, or enforce laws. The bicameral design, a result of the Great Compromise at the Constitutional Convention of 1787, balanced the demand for equal state representation (Senate) with representation based on population (House).
The mechanism of Congress is detailed in Article I of the Constitution, which vests all legislative powers in the institution. The House has 435 voting members elected for two-year terms, while the Senate has 100 members, two from each state, serving six-year terms. For a bill to become law, it must be approved by a majority vote in both the House and the Senate. Congress's enumerated powers, listed in Article I, Section 8, include the power to lay and collect taxes, regulate commerce, declare war, and make all laws "necessary and proper" for executing its powers.
The Congress is a key component of the U.S. system of separation of powers and checks and balances, connecting to the Executive Branch (President) and the Judicial Branch (Supreme Court). For example, the President can veto legislation, but Congress can override the veto with a two-thirds majority in both chambers. The Senate also has the unique power to ratify treaties and confirm presidential appointments. A recent change has been the continued expansion of executive authority, leading to a long-simmering frustration that Congress has struggled to assert its constitutional role as the primary policymaking branch. The number of Representatives was capped at 435 by the Reapportionment Act of 1929.