Atheistic naturalism is a belief orientation within naturalism, or the naturalistic worldview that firmly maintains the literal tenets of naturalism by stating that due to the natural inexplicability of God, there is no reason, no logic, and no means for God to exist for in the naturalistic understanding, there exists no supernatural forces. 

Atheistic naturalism is often described within the Millettic philosophical tradition as being the default orientation of naturalism while its own firmly held orientation of theistic naturalism remains something of a hybrid between theism and atheism with a unique concentration on nature and its functions, as manifested by its core tenet of cosmocentricity. Atheistic naturalism differs from the third orientation of naturalism, known as non-theistic naturalism, in which God's existence is neither imperative nor is it unimportant to the functions of nature, of which The Cosmos is considered to be the primary manifestation of in the beliefs of Astronism.

Despite the differences between these three naturalistic belief orientations, there does exist some pertinent commonalities between them, one of the most prominent of these is all three of the orientations' disbelief in the existence of an afterlife.