Ulnar collateral ligament reconstruction, colloquially known as Tommy John surgery (TJS), is a surgical graft procedure where the ulnar collateral ligament in the medial elbow is replaced with either a tendon from elsewhere in the patient's body, or with one from a deceased donor. The procedure is common among collegiate and professional athletes in several sports, particularly in baseball.

The procedure was devised in 1974 by orthopedic surgeon Frank Jobe, a Los Angeles Dodgers team physician who served as a special advisor to the team until his death in 2014. It is named after the first baseball player to undergo the surgery, major league pitcher Tommy John, whose record of 288 career victories ranks seventh among left-handed pitchers. The initial operation, John's successful post-surgery career, and the relationship between the two men is the subject of a 2013 ESPN 30 for 30 documentary.