Most cases are litigated in state courts and involve claims and defenses under state laws. In a 2012 report, the National Center for State Courts' Court Statistics Project found that state trial courts received 103.5 million newly filed cases in 2010, which consisted of 56.3 million traffic cases, 20.4 million criminal cases, 19.0 million civil cases, 5.9 million domestic relations cases, and 1.9 million juvenile cases. In 2010, state appellate courts received 272,795 new cases. By way of comparison, all federal district courts in 2010 together received only about 282,000 new civil cases, 77,000 new criminal cases, and 1.5 million bankruptcy cases, while federal appellate courts received 56,000 new cases.

Where are cases usually argued?