Parallel Federal and State Pyramids
The US has two distinct judicial hierarchies. State courts handle most criminal and civil cases: trial courts (district, circuit, or superior courts depending on state), intermediate appellate courts, and the state supreme court. Federal courts, in parallel, hear disputes over federal law, constitutional questions, bankruptcy, and cases between parties from different states. Both pyramids have trial judges at the bottom and appellate panels at the top. Most cases never leave their starting pyramid; a state contract dispute stays in state court even if federal law touches it, unless there is federal-question jurisdiction or diversity jurisdiction with the amount in controversy exceeding $75,000.
The Supreme Court (SCOTUS) sits at the apex of both systems. It reviews cases from either pipeline, granting cert to roughly 70 cases per year out of 7,000 petitions. Its decisions on federal law or constitutional rights bind all lower courts nationwide.
Why Two Systems, and Crossover Points
Federalism split power between states and the federal government, so courts were split too. States retained sovereign authority over their own courts and law, while federal courts were limited to their enumerated jurisdiction. In practice, crossover happens: a defendant in a state criminal case might petition federal court for habeas corpus review of a constitutional violation; a state court might abstain and let federal court hear a novel federal-law question first. The doctrine of Younger abstention lets federal courts decline cases to respect state court authority, while the reverse-Erie doctrine keeps state courts from deciding pure federal questions beyond their expertise.