NOTE (1)
The rules of squash are to apply except as follows:-
Singles

• Bounce the ball in the service box and strike the ball with an underarm action.
• Every rally scores a point (i.e., a point is added to the score when the rally is won by either the server or the receiver).
• The game is played to 15 points unless the score reaches 14 all when it is played to 16.
• Matches to be best of three games.
• When the receiver wins the rally he also wins the serve.

 NOTE (2)

• Lets and penalties are to apply as per the rules of squash.
• Lines marked on court walls and floor have the same significance as for squash.

Doubles

• Service as for singles.
• Every rally scores a point as for singles.
• The game is played to 15 or 16 points as for singles.
• The strikers alternate (Striker 1 is followed by Striker 2,then Striker 3 and Striker 4. Striker 1 and 3 play as a team against 2 and 4).

For more details, refer to the local or National Racquetball Association for further details.  In some countries the rules can vary slightly.