The official rules of tennis in the United States are those adopted by the United States Tennis Association. The USTA is a member of the International Tennis Federation and the ITF's rules apply to tennis matches in the U.S. Conduct is governed by "The Code" which has also been adopted by the USTA.
If you are looking for the USTA's tennis rules or for "The Code," just go to this page on the USTA's website. You'll find all of these materials plus some great commentary and explanation of specific provisions of the rules and The Code.