Lawn tennis was originally played on grass courts, but most major events are now played on courts of hard, composite materials; exceptions include Wimbledon, played on grass, and the French Open, played on clay. In singles play the court measures 78 ft by 27 ft (23.8 m by 8.2 m). The court is divided in half by a net 3 ft (91 cm) high in the middle and 3.5 ft (1.1 m) high at the end posts. On either side of the net lie the forecourts, each of which contains two adjacent service courts measuring 21 ft by 13.5 ft (6.4 m by 4.1 m) each. A backcourt 18 ft (5.5 m) long adjoins each forecourt. A base line that runs parallel to the net terminates the playing court. In doubles play, 41/2-foot-wide (1.4-m) alleys flanking either side of the court perpendicular to the net are also in play.
Play is directed toward hitting the inflated rubber, felt-covered, unstitched ball (slightly smaller than a baseball) with a racket—oval headed, originally 27 in. (68.58 cm) long but now usually longer, the hitting surface strung with resilient fiber—into the opponent's court so that it may not be returned. One player serves an entire game and is given two service tries each time the ball is put in play. The ball is served diagonally from behind the base line so that it bounces beyond the net, in the opposite service court. A let ball (one that caroms off the top of the net into the proper service court) does not count as a fault (bad serve). Service alternates after points, between the right- and left-hand courts. After the first game and all odd-numbered games, the players change ends of the court.
Once the serve puts the ball in play, players may hit it into any part of the opponent's court until a point is scored. Rallies won by either player score points. Scoring progresses from love (zero) to 15 (first point), to 30, then 40. The point scored after 40 wins the game, but when the game goes to deuce (tied at 40–40) a player must go two points ahead to win it. The first player to win six games takes the set, provided the opposing player has won no more than four games. Traditionally, after the players were tied at five games all, the first to go two games ahead won the set. In 1970, however, the United States Lawn Tennis Association (founded 1881 and now simply the United States Tennis Association), the sport's national governing body, initiated an abbreviated method, called the tie-breaker, for deciding deadlocked sets. In a tie-breaker, the first player to win seven points wins the set, provided the opponent trails by at least two points. Only in the deciding set of major championship matches outside the United States is the original two-game margin of victory retained. The best two out of three sets wins most professional matches; the best three out of five sets wins a late-round match in men's play in major championships. An umpire calls play, and in important matches a net judge, foot-fault judges, and linesmen often assist.