Tyler Hamilton (born March 1, 1971) is an American former professional road bicycle racer. He is the only American rider to win one of the five Monuments of cycling, taking Liège–Bastogne–Liège in 2003. Hamilton became a professional cyclist in 1995 with the US Postal Service cycling team. He was a teammate of Lance Armstrong during the 1999, 2000 and 2001 Tours de France, where Armstrong won the general classification. He was a key asset for Armstrong, being a very good climber as well as time-trialist. Hamilton appeared at the 2000 and 2004 Summer Olympics. In 2004, he won a gold medal at the individual time trial. The first doping test after his Olympic victory gave a positive result, but because the backup sample was frozen, no doping offence could be proven. After he failed further doping tests at the 2004 Vuelta a España, Hamilton was suspended for two years from the sport.

Hamilton came back after his suspension and became national road race champion in 2008. In 2009, Hamilton failed a doping test again, and was banned for eight years, which effectively caused him to retire. In July 2010, he was subpoenaed to appear before a grand jury for the use of performance-enhancing drugs in cycling. In May 2011, Hamilton admitted that he had used banned substances in competition, and returned his gold medal. In 2012, he co-authored a book The Secret Race: Inside the Hidden World of the Tour de France: Doping, Cover-ups, and Winning at All Costs, which details his doping practices and experience in the world of cycling. On August 10, 2012 the International Olympic Committee (IOC) stripped Hamilton of his 2004 gold medal.