Congress has two houses: the Senate and the House of Representatives. These houses have different procedural rules, and their members serve terms of different lengths. Senators were originally chosen by state legislatures, but now both senators and representatives are popularly elected. Reflecting the original compromise between the large states and the small states, each state has two senators, at least one representative, and each state has as many more representatives as its share of the national population, for a total of 435 representatives. Senators are elected from the entire state, and representatives are elected by districts, if the state has more than one representative. The districts for representatives are redrawn every 10 years after the national census.

Congress is the only branch of government that can authorize the spending of government funds and the imposition of taxes. Each proposed law (bill) must be passed by both houses of Congress. The president can veto legislation he or she does not like, and Congress can override a presidential veto only by a two- thirds majority vote of both houses. The president also can propose legislation and does so each year when he or she presents the proposed budget. Ultimately, however, it is Congress that passes laws. To keep Congress from becoming too powerful, the Constitution gave the power to enforce the laws to the president.