Pantheism, simply stated, means "God is All". It is the view that everything is of an all encompassing God. More detailed definitions tend to emphasize the idea that natural law, existence and/or the universe (the sum total of all that is was and shall be) is personified in the theological principle of 'God'.
One way to describe certain interpretations of pantheism is to say "you are to God, as an individual blood cell in a your vein is to you." While a cell may be aware of its own environs, and even has some choices (freewill) between right and wrong (killing a bacteria, becoming cancerous, or perhaps, just doing nothing, among countless others) it has little conception of the greater being of which it is a part. This conception of God can be seen as included within Brahman Hinduism. It is important to note, however, that not all modern interpretations of pantheism would find this analogy meaningful, and for that matter, not even all pantheists believe in free will. This is indicative of a wide diversity of pantheist belief which will be explored throughout this article.
Pantheism is often attacked as tautology by atheists, since it appears to many of them to do little more than re-define the word 'God' to mean 'world' or 'universe'. It should be noted, however, that there is no significant agreement that making God synonymous with universe must necessarily make either term any less meaningful. Pantheists maintain that such an arrangement serves to create both a new and a potentially far more insightful conception of both of these terms.
Perhaps the most significant debate within the pantheistic community is as to the nature of God. Some (classical pantheism) believe in a personal, conscious, and omniscient deity, and see this deity as uniting all true religions. Others, some being within (Naturalistic Pantheism) believe in a unconscious, non-sentient universe, which while being holy and beautiful, is only seen as being a God in an extremely non-traditional impersonal sense.
Of course, the viewpoints encompassed within the pantheistic community are necessarily diverse, but the central ideas of the universe being an all encompassing unity, a common purpose, and the sanctity of both nature and its natural laws are found throughout.
A few of the more notable people who have held pantheistic world-views include Albert Einstein, Giordano Bruno and Johann Wolfgang von Goethe amongst many others of note throughout Human history.