John Patrick McEnroe Jr. (born February 16, 1959) is an American former professional tennis player. He was known for his shot-making and volleying skills, his rivalries with Björn Borg and Jimmy Connors, and his confrontational on-court behavior, which frequently landed him in trouble with umpires and tennis authorities.

McEnroe is the only male player in tennis history to hold the world No. 1 ranking in both singles and doubles simultaneously. Only one other male player, Stefan Edberg, ever attained No. 1 in both, although at different times. McEnroe finished his career with 77 singles titles on the ATP Tour and 78 doubles titles; this remains the highest men's combined total of the Open Era. He is the only male player to win more than 70 titles in both the men's singles and the men's doubles categories. He also won 25 singles titles on the ATP Champions tour. He won seven Grand Slam singles titles (four at the US Open and three at Wimbledon), nine Grand Slam men's doubles titles (five at Wimbledon and four at the US Open), and one Grand Slam mixed doubles title (at the French Open). His singles match record of 82–3 in 1984 remains the best single season win rate of the Open Era.

McEnroe also excelled at the year-end tournaments, winning eight singles and seven doubles titles, both of which are records. Three of his winning singles year-end championships were at the Masters Grand Prix (the ATP year-end event) and five were at the World Championship Tennis (WCT) Finals, an event which ended in 1989. Since 2000, there has been only one year-end men's singles event, the ATP Finals (the new name for the Masters Grand Prix). He was named the ATP Player of the Year and the ITF World Champion three times each: 1981, 1983 and 1984.

McEnroe contributed to five Davis Cup titles for the U.S. and later was team captain. He has stayed active in retirement, often competing in senior events on the ATP Champions Tour. He also works as a television commentator during majors tournaments.