Marion Lois Jones, also known as Marion Jones-Thompson (born October 12, 1975 in Los Angeles, California), is an American former world champion track and field athlete. She won five medals at the 2000 Summer Olympics in Sydney, Australia but has since agreed to forfeit all medals and prizes dating back to September 2000 after admitting that she took performance-enhancing drugs.

In October 2007, Jones admitted she doped, having taken steroids before the Sydney 2000 Summer Olympics and acknowledged that she had, in fact, lied when she previously denied steroid use in statements to the press, to various sports agencies, and—most significantly—to two grand juries. One impaneled to investigate the BALCO "designer steroid" ring, and the other impaneled to investigate a check fraud ring involving many of the same parties from the BALCO case. As a result of these admissions, Jones accepted a two-year suspension from track and field competition, and announced her retirement from track and field on October 5, 2007.

The United States Anti-Doping Agency stated that the sanction "also requires disqualification of all her competitive results obtained after September 1, 2000, and forfeiture of all medals, results, points and prizes". On October 5, 2007, Jones formally pled guilty to lying to federal agents in the BALCO steroid investigation in the U.S. District Court. On January 11, 2008, Jones was sentenced to 6 months in jail. She began her sentence on March 7, 2008 and was released on September 5, 2008.