According to wikipedia.org:
Atheism, in its broadest sense, is an absence of belief in the existence of any deities. That is, all who do not have such a belief?whether they are nontheists, agnostics, or even Buddhists?are covered under this term. Atheism can also be defined more narrowly as the active rejection of the existence of gods, either of a specific or general kind, or even that gods can exist. Generally speaking, atheism refers to a lack of belief in all deities for any reason.
Although atheists often share common concerns regarding empirical evidence and the scientific method of investigation and a large number are skeptics, there is no single ideology that all atheists share. Additionally, there are atheists who are religious or spiritual, though many of these would not describe themselves as atheists.
A question I was asked about Atheism being listed under religions:
Are you saying atheism is a religion?
There are a lot of gray areas here and i am going to try to keep my personal opinions out of this answer.
According to the American Atheists Organization (www.atheists.org):
Since 1963, AMERICAN ATHEISTS has been the premier organization laboring for the civil liberties of Atheists, and the total, absolute separation of government and religion. It was born out of a court case begun in 1959 by the Murray family which challenged prayer recitation in the public schools. That case ? Murray v. Curlett ? was a landmark in American jurisprudence on behalf of our First Amendment rights. It began: "Your petitioners are Atheists, and they define their lifestyle as follows. An Atheist loves himself and his fellow man instead of a god. An Atheist accepts that heaven is something for which we should work now ? here on earth ? for all men together to enjoy. An Atheist accepts that he can get no help through prayer, but that he must find in himself the inner conviction and strength to meet life, to grapple with it, to subdue it and to enjoy it. An Atheist accepts that only in a knowledge of himself and a knowledge of his fellow man can he find the understanding that will help to a life of fulfillment."While not following a higher power, it is none-the-less a faith. In this case a faith that what we have here, in this life, is all that there is.
However, the 'clincher', if you will, that says we must include Atheism as a religion is that while the group may openly say they are not a religion. They file law suits stating that their religious freedoms are being violated.
This is copied from atheists.org (http://www.atheists.org/flash.line/court36.htm):
August 28, 2005
WHOSE FIRST AMENDMENT IS IT, ANYWAY?"
CIRCUIT COURT RULES FOR PRISON INMATE'S GROUP, ATHEISM A RELIGION
A federal court has ruled that prison officials in Wisconsin violated the rights of an inmate who sought to form an Atheist discussion group because they failed to treat Atheism as a religion.
The article later says that.
The Seventh US Circuit Court of Appeals, however, ruled last week that the prison violated Kaufman's civil rights by not considering atheism as a religion and protected form of religious expression.
If they are going to sue on religious grounds then it seems Atheism must be considered a religion.
As far as a federal ruling of what is a religion, The Civil rights Act of 1964 states:
"To be a bona fide religious belief entitled to protection under either the First Amendment or Title VII, a belief must be sincerely held, and within the believer's own scheme of things religious."
(USCA Const. Amend 1: Civil Rights Act 1964 701 et seq., 717 as amended 42 USCA 2000-16)
To the best of my knowledge that ruling still stands.
Thus, unless one can prove that a person does not really believe something, then yes it is legally a religion . . . right, wrong, or indifferent.