Is atheism a religion? Austin Cline puts it simply:

The truth is that atheism lacks every one of the basic characteristics of religion. … It can be part of a religion, but it can’t be a religion by itself. They are completely different categories: atheism is the absence of one particular belief while religion is a complex web of traditions and beliefs. They aren’t even remotely comparable.

And he has another, sharper point that I have never heard before:

Not even theism alone can qualify as a “religion” under even the broadest definitions.

Think about that the next time someone tells you that atheism is a religion. Theism is not a religion. Not all by itself. It has to be mixed up with a “complex web” of other stuff before it becomes a religion. Cline calls this stuff “traditions and beliefs”, which is not quite right — but the larger point is very good. Atheism is a philosophical position, as is theism. Neither one is anything like a religion.