You Cannot Be Serious is a book written by the world's former #1 tennis

Tennis

Tennis is a sport usually played between two players or between two teams of two players each . Each player uses a racket that is strung to strike a hollow rubber ball covered with felt over a net into the opponent's court. Tennis is an Olympic sport and is played at all levels of society at all...

 player John McEnroe

John McEnroe

John Patrick McEnroe, Jr. is a former world no. 1 professional tennis player from the United States. During his career, he won seven Grand Slam singles titles , nine Grand Slam men's doubles titles, and one Grand Slam mixed doubles title...

 (with James Kaplan).

McEnroe details life behind the scenes on the tennis tour as well as giving the reader a very candid look at his personal life and struggles. The book made it to the top of the New York Times bestseller list.
The hardcover edition was published by G.P. Putnam's Sons in 2002, with the paperback

Paperback

Paperback, softback or softcover describe and refer to a book by the nature of its binding. The covers of such books are usually made of paper or paperboard, and are usually held together with glue rather than stitches or staples...

 being released a year later by The Berkley Publishing Group

Berkley Books

Berkley Books is an imprint of Penguin Group that began as an independent company in 1955. It was established by Charles Byrne and Frederic Klein, who were working for Avon and formed "Chic News Company". They renamed it Berkley Publishing Co. in 1955. They soon found a niche in science fiction...

 in the USA, and by Time Warner

Time Warner

Time Warner is one of the world's largest media companies, headquartered in the Time Warner Center in New York City. Formerly two separate companies, Warner Communications, Inc...

in the UK. The name of the book comes from McEnroe's famous catchphrase "You Cannot Be Serious!"