. . . from the USTA web site (www.usta.com) under Rules/Officials -> Rules of Tennis -> Rule # 27.

The following system shall be used in a tie-break game.

Singles
i. A player who first wins seven points shall win the game and the set provided he leads by a margin of two points. If the score reaches six points all the game shall be extended until this margin has been achieved. Numerical scoring shall be used throughout the tie-break game.
ii. The player whose turn it is to serve shall be the Server for the first point. His opponent shall be the Server for the second and third points and thereafter each player shall serve alternately for two consecutive points until the winner of the game and set has been decided.
iii. From the first point, each service shall be delivered alternately from the right and left Courts, beginning from the right Court. If service from a wrong half of the Court occurs and is undetected, all play resulting from such wrong service or services shall stand, but the inaccuracy of station shall be corrected immediately it is discovered.
iv. Players shall change ends after every six points and at the conclusion of the tie-break game.
v. The tie-break game shall count as one game for the ball change, except that, if the balls are due to be changed at the beginning of the tie-break, the change shall be delayed until the second game of the following set.

Doubles
In doubles the procedure for singles shall apply. The player whose turn it is to serve shall be the Server for the first point. Thereafter each player shall serve in rotation for two points, in the same order previously in that set, until the winners of the game and set have been decided.

Rotation of Service
The player (or pair in the case of doubles) whose turn it was to serve first in the tie-break game shall receive service in the first game of the following set.

. . . from the USTA web site (www.usta.com) under Rules/Officials -> Rules of Tennis -> Rule # 27.