Pantheism holds that God is identical with the real world. God is all and all is God. God does not transcend reality but is immanent in reality, or rather, all reality is in God. Beyond him is only illusion or nonreality.  It is the personal feeling that everything is or contains God, and God is everything or all. The concept that God is immanent in all things is one of the oldest intuitions found in humankind. However, pantheism never developed into a formal doctrine.

Pantheism is the polar opposite of Deism. Where Deism stresses God's transcendence, Pantheism stresses his immanence in the world.  The earliest evidence of pantheism is found on Brahmanism, the oldest existing religion, in the Vedas, dating back to 1000 BC.  It is associated with the Egyptian religion when Ra, Isis and Osiris were identified with all existence.

The book recognized as containing the most complete attempt at explaining and defending pantheism from a philosophical perspective is Spinoza's Ethics, finished in 1675 two years before his death. In 1720 John Toland wrote the Pantheisticon: or The Form of Celebrating the Socratic-Society in Latin. He (possibly) coined the term "pantheist" and used it as a synonym for "Spinozist." However, aside from some interesting pantheistic sounding slogans (like "Every Thing is to All, as All is to Every Thing"), and despite promising "A short Dissertation upon a Two-fold philosophy of the Pantheists" Toland's work has little to do with pantheism.

Even with these definitions there is dispute as to just how pantheism is to be understood and who is and is not a pantheist.  Many philosophical scholars think the great Greek philosopher Parmanides was a pantheist as well as Plotinus, Erigen, and Spinoza.  Other possible pantheists include some of the Presocratics, Plato; Lao Tzu, Plotinus, Schelling, Hegel, Bruno, Eriugena and Tillich.

The sentiment or belief in pantheism have predominantly influenced the thoughts and works of many poets, philosophers, mystics, and extremely spiritual people.  Possible pantheists among literary figures include Goethe, Coleridge, Wordsworth, Emerson, Whitman, D.H. Lawrence, and Robinson Jeffers.  Many modern poets consider pantheism existing in their world-view.  Beethoven (Crabbe 1982) and Martha Graham (Kisselgoff 1987) have also been thought to be pantheistic in some of their work--if not pantheists.

 In literature it is often seen as a an ardent faith in nature as both the revelation of deity and deity itself, as can be illustrated with a few lines from Wordsworth's Lines Composed a Few Miles above Tintern Abbey:

 

. . . a sense sublime  Of something far more deeply interfused,  Whose dwelling is the light of setting suns,  And the round ocean and the living air  And the blue sky, and in the mind of man;  A motion and a spirit, that impels  All thinking things, all objects of all thought,  And rolls through all things.