Under the principles of federalism embodied in the Constitution, state, not federal, courts are the principal trial courts. This point is made most clearly by the express limits, contained in Article III, on which cases can be heard at all in the federal courts.

In addition, Congress has the power to further constrain the types of cases that federal courts can hear, as it has done by restricting diversity of citizenship cases to those in which the amount in controversy exceeds $75,000. The result is that while only about 400,000 cases are filed in federal trial courts each year, approximately 100 million cases go to state courts.