Thelema (Greek for Will) is the magickal system that has evolved from Aleister Crowley's magickal writings. It is a complete system of philosophy, magick (and even religion).
The core ideas of Thelema are that "Every Man and Every Woman is a Star", and that "thou hast no right but to do thy will. Do that and no other shall say nay.". They are encapsulated in the greeting "Do what thou wilt shall be the whole of the Law" and its response "Love is the Law, Love under Will". These are, on first appearance, very free directions leading potentially to anarchy. On closer examination this is not neccessarily the case. The fact that everyone has no right but to do their will (that is, their nature rather than whatever impulse takes them at any instant) means that everyone must first discover what their will is (a harder thing to do than it sounds!).
Thelema also has deities of its own. They represent universal forces which occupy much Magickal and mystical experience:
Nuit, the azure bodied goddess of the night sky,
is a goddess of infinite space, of the void.
Hadit is the god of the infinitely small but omnipresent point of energy.
Therion, the male principle, is represented as a lion headed, serpent bodied beast.
Babalon, the female principle, is the "scarlet woman", the free-loving "woman girt with a sword".
Ra-Hoor-Khuit, the crowned and conquering child, is the solar god, Ra and the god of war, Horus. He also has a silent aspect, Har-Poor-Kraat. Together they represent the war-like but increasingly intuitive current of the present aeon of Aquarius.
A further goddess, Maat, the goddess of truth, balance and justice, although not one of the original deities in the Thelemic pantheon, has begun to play an important part in Thelemic thought. It has been suggested that the forces and trends associated with Maat have started to manifest in the present Aeon. For further information on this see "Maat Magick" by Nema.