Steven Jay Hatfill (born October 24, 1953) is an American physician, virologist and bio-weapons expert. The US Department of Justice identified the former government scientist as a "person of interest" in its investigation of the 2001 anthrax attacks. FBI raids on his home were well-attended by journalists and, consequently, several news outlets speculated that Hatfill was at one time the likely suspect for the attacks. He later sued the government for ruining his reputation, a case which the government settled for US$5.8 million. Investigators later announced that the anthrax attacks had been carried out by another government scientist, Bruce Edwards Ivins, whom they concluded had acted alone.

Hatfill was born in Saint Louis, Missouri, and graduated from Mattoon Senior High School, Mattoon, Illinois (1971), and Southwestern College in Winfield, Kansas (1975), where he studied biology. During college he took a year off and worked with a Methodist medical missionary in Kapanga, Zaire. (His mentor was Dr. Glenn Eschtruth, whose daughter Caroline he later married and divorced.)

Hatfill served as an enlisted soldier in the U.S. Army in the late 1970s. (In 1999, he would tell a journalist during an interview that he had been a "captain in the U.S. Special Forces", but in a subsequent investigation the Army stated that he had never served with the Special Forces.)