The following ITF Rules of Tennis and Cases and Decisions are the official rules of the International Tennis Federation (ITF), of which the United States Tennis Association (USTA) is a member. USTA Comments have the same weight and force in USTA tournaments as do ITF Cases and Decisions. When a match is played without officials, The Code shall apply in any situation not covered by the ITF Rules of Tennis. Except where otherwise stated, every reference in the ITF Rules of Tennis to the masculine includes the feminine gender. 
Read The ITF Rules of Tennis.

Friend at Court: The USTA Handbook of Tennis Rules and Regulations

The International Tennis Federation (ITF) is the governing body of the game of tennis and its duties and responsibilities include determination of the ITF Rules of Tennis. To assist the ITF in carrying out this responsibility, the ITF has appointed a Rules of Tennis Committee which continually monitors the game and its rules, and when considered necessary makes recommendations for changes either on a permanent basis or for a limited trial period to the Board of Directors of the ITF who in turn make recommendations to the Annual General Meeting of the ITF which is the ultimate authority for making any changes to the Rules of Tennis.

Have you ever had a dispute with a fellow player over a call on the court that you couldn’t settle? Or have you ever wondered why a certain ruling was made during a match you were watching? Maybe you’re just curious about how some scenarios, from the common to the ridiculous, are resolved. The USTA constantly receives these types of questions from players and fans, so we figured it’s about time we provided a forum in which queries about rules can be answered. Visit the Improve Your Game homepage for The Final Word.