What is Atheism?

Atheism is not a religion, but more a philosophy. It is the lack of belief in the existence of God or Gods.
Atheists have analyzed the available material evidence of the existence of one or more deities and has concluded that there is no real evidence of any Gods or Goddesses. They believe that the universe, Earth and its life probably evolved by perfectly natural processes, without intervention by a supernatural entity.
They generally feel that ethical and moral systems governing human behavior can be developed without reference to any code of behavior of allegedly divine origin. Other Atheists have simply never been exposed to belief in a deity or deities and therefor have no belief in them.