Philip Barton Key II was an American lawyer who served as U.S. Attorney for the District of Columbia. He is most famous for his public affair with Teresa Bagioli Sickles, and his eventual murder at the hands of her husband, Congressman Daniel Sickles of New York. Sickles defended himself by adopting a defense of temporary insanity, the first time the defense had been successfully used in the United States.

The United States attorney for the District of Columbia (USADC) is responsible for representing the federal government in the United States District Court for the District of Columbia. The U.S. Attorney's Office for the District of Columbia has two divisions, the Civil Division and the Criminal Division. The Civil Division is responsible for representing federal agencies in the U.S. District Court for the District of Columbia and in appeals before the U.S. Court of Appeals for the District of Columbia Circuit.