Pantheism is the belief that the universe and nature are divine.
Every religion has had its pantheists. Pantheism is the perennial religion, which continually emerges from all transcendental or idealist religions.
In addition people in every religion have seen God in nature, whether they formally express that identity or not. Examples include Shaftsbury, Rousseau, and many poets from Wordsworth to Robinson Jeffers.
Pantheism has taken many diverse forms. Strict or scientific pantheism holds that God and the material universe are identical. Its first adherents were the Greek materialist Heraclitus, the Chinese Taoist Chuang Tzu, and the Stoic philosopher Zeno of Cittium. Later proponents have included the Christian David of Dinant, the neo-Confucian Chang Tsai, and the author of these pages, Paul Harrison. Taoism is a form of materialist pantheism, as are some types of Mahayan Buddhism.
There have been many other types of pantheism. All of them identify God in some way with what is considered most fundamental in the Universe.
Some pantheisms are idealistic or world-negating - believing that the visible world is unreal or an illusion, masking an underlying unity. These include the Eleatic school of Xenophanes and Parmenides, the Upanishads, and most schools of Mahayana Buddhism.
Related to pantheism, and included in this history, is panentheism. Panentheists believe that God is present in the sensible universe, but also extends beyond it. These include the neo-Platonist Plotinus and most Christian and Islamic pantheists such as Meister Eckhart, Ibn Al'Arabi or Attar.
Many panentheists, while accepting that the material world exists, are world-rejecting, believing that the material world is in some way separate from and inferior to the spiritual world. A common view is that the body is the prison of the soul, which can only be liberated if it suppresses the body's needs, and only fully liberated after death.
The world-negating and world-rejecting pantheisms are as distant from scientific pantheism as it is possible to get. In a sense they are the reverse of pan-theism - "everything=God" - in that they deny or denigrate the "everything" part of the equation, at least in any normal sense of the word "everything." They despise or deny the world of the senses and of the body. They are included in this history for completeness - and to remind us of pitfalls to avoid.