I read a book on Wicca that says "all Wiccans must do this and never do that," and then I read another one that said Wiccans can make their own rules. Some people believe in the Threefold Law, and others don't. Others say that the Wiccan Rede is only for Wiccans but not other Pagans. What's going on here? Are there rules in Wicca or not?
The word "rules" can be a puzzling one, because while there are guidelines, they do tend to vary from one tradition to another. In general, most Wiccans and other Pagans follow some set of rules that is unique to their own tradition - however, it's important to note that these standards are not universal. In other words, what Group A holds true as law cannot be applied towards Group B.
The Wiccan Rede
Many groups, particularly NeoWiccan ones, follow one form or another of the Wiccan Rede, which says, "An' it harm none, do as you will." This means that you can't intentionally or knowingly cause harm to another person. Because there are so many different forms of Wicca, there are dozens of different interpretations of the Rede. Some people believe it means you can't hunt or eat meat, join the military, or even swear at the guy who took your parking spot. Others interpret it a bit more liberally, and some believe that the rule of "harm none" doesn't apply to self-defense.
The Rule of Three
Many traditions of Paganism, including most variations of Wicca, believe in the Law of Threefold Return. This is essentially a karmic payback - anything you do comes back to you three times more intensely. If good attracts good, then guess what bad behavior brings you?
The 13 Principles of Wiccan Belief
In the 1970s, a group of witches decided to assemble a cohesive set of rules for modern witches to follow. Seventy or so individuals from a variety of magical backgrounds and traditions got together and formed a group called the American Council of Witches, although depending on who you ask, they are sometimes called the Council of American Witches. At any rate, this group decided to try to assemble a list of common principles and guidelines that the entire magical community could follow. These principles are not adhered to by everyone, but are often used as a template in many sets of coven mandates.
In the 1950s, when Gerald Gardner was writing what eventually become the Gardnerian Book of Shadows, one of the items he included was a list of guidelines called the Ardanes. The word “ardane” is a variant on “ordain”, or law. Gardner claimed that the Ardanes were ancient knowledge that had been passed down to him by way of the New Forest coven of witches. Today, these guidelines are followed by some traditional Gardnerian covens, but are not often found in other NeoWiccan groups.
In many traditions, each coven is responsible for establishing its own set of bylaws or mandates. Bylaws may be created by a High Priestess or High Priest, or they may be written by a committee, depending on the rules of the tradition. Bylaws provide a sense of continuity for all members. They typically cover things like standards of behavior, principles of the tradition, guidelines for acceptable use of magic, and an agreement from members to abide by those rules.
Finally, keep in mind that your own sense of magical ethics should be a guideline to you as well. You can't enforce your rules and ethics on other people, though -- they have their own set of laws to follow, and those may be different from your own. Remember, there's no Big Pagan Council that sits and writes you a Bad Karma Ticket when you do something wrong. Pagans are big on the concept of personal responsibility, so ultimately it's up to you to police your own behavior, accept the consequences of your own actions, and live by your own ethical standards.