A serve (or, more formally, a service) in tennis is a shot to start a point. A player will hit the ball with a racquet so it will fall into the diagonally opposite backside box without being stopped by the net. Normally players begin a serve by tossing the ball into the air and hitting it (usually near the highest point of the toss). The ball can only touch the net on a return and will be considered good if it falls on the opposite side. If the ball contacts the net on the serve but then proceeds to the proper backside box, it is called a let; this is not a legal serve in the major tours (but see below) although it is also not a fault. Players typically serve overhead, but serving underhand, although rare, is allowed. The serve is the only shot a player can take their time to set up instead of having to react to an opponent's shot.
The serve is one of the more difficult shots for a novice, but once mastered it can be a considerable advantage. Advanced players can hit the serve in many different ways and often use it as an offensive weapon to gain an advantage in the point or to win it outright. Because of this, professional players are expected to win most of their service games, and the ability to break an opponent's serve plays a crucial role in a match.
Since the server has the advantage of being the initial aggressor, for his opponent to return the ball and so keep it in play often involves the defensive endeavor of minimizing the opponent's advantage. This may involve simply lunging to get the racket on the ball before it passes. If a controlled return of service is possible, a hard groundstroke to one side or the other of the opponents's baseline may be performed. If the server rushes the net immediately upon hitting the serve, the returner has several options: return the ball at the feet of the server not far past the net, forcing him to hit a half volley (which is hard to do aggressively); lob the ball over the rushing server's head; or hit a passing shot hard and low over the net too far to the left or right for the server to hit it.