• You lose the point if you double-fault.big serve in tennis image by jimcox40 from Fotolia.com
  
  The service in a tennis match begins when the server’s feet are at rest behind the baseline and ends when the server either hits or misses the ball. The server tosses the ball in the air and attempts to hit it. There are no restrictions on the movement of the ball and racket, and servers can even serve underhand if they choose, but there are rules that can render an attempted service unsuccessful.
  
  

Choice of Service

• Before a match begins, the order of service is determined by a coin toss. The winner chooses whether she would like to serve first or second, or can pass off that decision to the other player and instead choose which side of the court she would like to play on first. After each game, the service switches to the opposing player.
  
  

Service Fault

• According to the Unites States Tennis Federation (USTA) rule book, a service fault occurs when the server breaks certain rules relating to the service. For example, if the server swings and misses the ball, a service fault will be called. In addition, the server commits a fault if the serve hits his partner (in a doubles match), or hits a permanent fixture on the court, such as the net post, before hitting the ground.
  
  

Second Service

• A service fault results in an immediate replay of the point, which is called a second service. The server remains on the current side of the court and serves again. If the server commits two consecutive faults, called a "double fault," the server loses the point.
  
  

The Let

• A service let occurs when the served ball hits the net, strap or band before landing in the receiver's service court. Although the serve may appear to be in play, a let is called because it hit the net. A let is also called if the server serves the ball before his opponent is ready. Like a service fault, the let allows the server to serve again, but a let does not count against the server and there is no limit to the number of lets a server can have in one point.