Note to Wiccans: Wicca isn't my path. I wrote this node based on my researches as a seeker. If you can write something I think is better, I will happily bow to your knowledge.

Wicca is the general term for Pagan religious groups descended from Gerald Gardner's original version of a modern witchcraft created in the 1940s and 1950s. Supposedly, Gardner was initiated into a family tradition (famtrad) by "Old Dorothy Clutterbuck". He found the rituals fragmentary and used his O.T.O. knowledge to flesh them out. The resulting rituals have a strong ceremonial magic feel, with obvious ties to The Lesser Banishing Ritual of the Pentagram. It is considered quite likely that the true source of the rituals is mostly Gardner, creating a syncretic religion all his own. Wicca in general is duotheistic (God and Goddess, who contain within them all other gods and goddesses), nature-oriented, sex-positive, magic-using, and focused on a mystery religion-type initiation. Each Wiccan is clergy, meaning that each member deals directly with deity (relating back to the initiatory route). Diety is considered immanent in the universe. Of course, some of these are pushed and bent within different groups detailed under Traditions below.

Some History and Myths
Gardner claimed that his tradition was an unbroken line, going all the way back to Margaret Murray's Goddess worship in paleolithic times. These claims have since been disproven, and are generally considered to be more of a myth (if not useless) within most covens. Historically, Wicca required initiation by an initiated witch (leading to the question "Who initiated the first witch?") and was heterosexist. These factors are not as common today, but are still present in the attitudes of some Wiccans. It is commonly thought that Wiccan means wise one in Old English or Latin; it appears that, in general, a stronger claim is made for it meaning "one that bends things to one's will." The equivalent for "wise one" appears to be wysard, which comes to us as wizard today.

Ethical Guidelines
Wicca's morals are usually encapsulated by a statement referred to as the Wiccan Rede -- "Do as you will, An' it harm none." This statement should not be confused with Aleister Crowley's famous statement. The Threefold Law, that what you do will return to you three times, adds a karmic touch. Wicca doesn't have large sets of rules, which makes many people think that it's a "do what you want" philosophy. However, the importance is on the practicioner's thinking about their actions, not whether or not they're covered by a given rule. Parallels can be drawn, naturally, between the Rede and the Golden Rule.

Wicca tends towards being an inclusive religion. However, within this inclusiveness there are many different Traditions, roughly analogous to Protestant Denominations. Some of these traditions are:

The Witches' Voice, at, is an excellent resource.
Wicca: A guide for the Solitary Practicioner, by Scott Cunningham, is considered one of the best introductions to Wicca.
Drawing Down the Moon, by Margot Adler, has a good overview of some of the different traditions of Wicca and Wicca's upsurge within the Pagan movement.