The God Delusion is a book published by Richard Dawkins in 2006. It contains arguments for the non-existence of God. The God Delusion was and is a best seller, has been for many years and is a prime example of New atheism.
Dawkins is one of today's most vocal advocates for atheism and his new book is a potent expression of a growing atheist viewpoint. While this book will almost certainly offend some believers, it will also bring relief to many skeptics. 
The book does a great deal to encourage readers to apply Critical thinking and avoid accepting religious claims on faith. The book also shows readers that they can be comfortable about religious doubt, and further that they can feel comfortable following Humanist morality rather than Christian morality.
Unsurprisingly many Christians hate this book, Christians can't even enjoy a good drink after copying impure text from The God Delusion. 
- Yes, that’s true, scientists actually did a test, see Gross gods and icky atheism