This article is from the Atheism FAQ, by mathew email@example.com with numerous contributions by others.
There are many philosophical justifications for atheism. To find out
why a particular person chooses to be an atheist, it's best to ask
Many atheists feel that the idea of God as presented by the major
religions is essentially self-contradictory, and that it is logically
impossible that such a God could exist. Others are atheists through
scepticism, because they see no evidence that God exists.
There are a number of books which lay out a philosophical
justification for atheism, such as Martin's "Atheism: A Philosophical
Justification" and Smith's "Atheism: The Case Against God". A few such
books are in the document listing "Atheist Media".
Of course, some people are atheists without having any particular
logical argument to back up their atheism. For some, it is simply the
most comfortable, common sense position to take.