Atheism is, almost by definition, not an organization; its defining characteristic – lack of belief in any God or gods – rests on a principle of questioning dogmatism and authority. Although atheists do organize, such organization is generally quite informal.
Although there are national atheist groups with local chapters, these are not officially representative of "atheism" in the same way that e.g. Catholic bishops officially represent the Catholic Church – there is no official "atheism" which can accept or reject members the way the Catholic Church can confirm or excommunicate its members.
It is therefore erroneous or misleading to speak of atheism as a centralized group, much less a religion.
- how atheism is the opposite of religion
- list of atheist organizations