What are the three branches of government and what does each do?

The legislative branch, Congress, writes laws, controls federal spending and taxation, declares war, and confirms senior appointments through the Senate. The executive branch, headed by the president and including the federal agencies and military, enforces and implements laws, conducts foreign policy, and issues regulations within statutory authority. The judicial branch, the Supreme Court and lower federal courts, resolves disputes and interprets the law and the Constitution, including the power of judicial review, established in Marbury v. Madison in 1803, to strike down laws and executive actions it finds unconstitutional.

Separation of powers works through checks. Congress passes laws but the president can veto them; Congress can override with two-thirds. The president appoints judges and officials but the Senate confirms. The courts can invalidate legislation, but Congress can rewrite laws, propose constitutional amendments, and shape federal court jurisdiction, and it controls the funding every branch depends on. Congress can impeach and remove executive and judicial officers. The friction is intentional, designed by framers more worried about concentrated power than about efficiency. Two persistent tensions in modern practice: much lawmaking effectively happens through agency regulation under broad statutory delegations, and Congress has ceded significant war and emergency powers to the executive over the past century, both of which are live constitutional debates rather than settled questions.