The 94 United States district courts are the general trial courts of the United States federal court system. Both civil and criminal cases are filed in the district court, which is a court of law, equity, and admiralty. There is a United States bankruptcy court associated with each United States district court. Each federal judicial district has at least one courthouse, and many districts have more than one. The formal name of a district court is "the United States District Court for" the name of the district—for example, the United States District Court for the Southern District of New York.

In contrast to the Supreme Court, which was established by Article III of the Constitution, the district courts were established by Congress. There is no constitutional requirement that there be any district courts at all. Indeed, after the ratification of the Constitution, some opponents of a strong federal judiciary urged that the federal court system be limited to the Supreme Court, which would hear appeals from state courts. This view did not prevail, however, and the first Congress created the district court system that is still in place today.

There is at least one judicial district for each state, the District of Columbia, and Puerto Rico. District courts in three insular areas—the United States Virgin Islands, Guam, and the Northern Mariana Islands—exercise the same jurisdiction as Article III U.S. district courts. Despite their name, these courts are technically not "District Courts of the United States." Judges on these Article IV territorial courts do not enjoy the protections of Article Three of the Constitution, and serve terms of ten years rather than for life.

There are 89 districts in the 50 States, with a total of 94 districts including territories.