Dawkins has argued against creationist explanations of life in his previous works on evolution. The theme of The Blind Watchmaker, published in 1986, is that evolution can explain the apparent design in nature. In The God Delusion he focuses directly on a wider range of arguments used for and against belief in the existence of a god (or gods).
Dawkins identifies himself repeatedly as an atheist, while also pointing out that, in a sense, he is also agnostic, though "only to the extent that I am agnostic about fairies at the bottom of the garden".
Dawkins had long wanted to write a book openly criticising religion, but his publisher had advised against it. By the year 2006, his publisher had warmed to the idea. Dawkins attributes this change of mind to "four years of Bush". By that time, a number of authors, including Sam Harris and Christopher Hitchens, who together with Dawkins were labelled "The Unholy Trinity" by Robert Weitzel, had already written books openly attacking religion. According to the Amazon.co.uk retailer in August 2007, the book was the best-seller in their sales of books on religion and spirituality, with Hitchens's God is Not Great: How Religion Poisons Everything coming second. This led to a 50% growth in that category over the three years to that date.
As of January 2010, the English version of The God Delusion had sold over 2 million copies. As of September 2014, it increased to 3 million copies. It was ranked second on the Amazon.com best-sellers' list in November 2006. It remained on the list for 51 weeks until 30 September 2007. The German version, entitled Der Gotteswahn, had sold over 260,000 copies as of 28 January 2010.