The Wiccan Rede
The Wiccan Rede is one of the major tenets of the Wiccan religion. The substance of the Rede is generally summarized in the last verse:
"Eight words the Wiccan Rede fulfill, "An it harm none do what ye will."
Or, in more modern English, "The Wiccan Rede is comprised of eight words: Do whatever you want as long as you harm no one." (Of course, it's no longer eight words in modern English.) Different sects of Wiccans read "none" differently: some include the self, others include animals, other plants, and so forth.
According to the Wiccan religion, the Rede was set in place by deities at the creation of the world (or earlier). The law was instated so that Wiccans would know the line between right and wrong and have a source of justice, as many sects of Wiccanism have no central authority or single deity who is the final arbiter.
There are many different versions of the Wiccan Rede but they are all more or less paraphrases of the last verse.
Interestingly, the ethics espoused in the Rede have gained quite a bit of modern currency among anarchists and some libertarians, and have become widely used in debates over, e.g., drug legalization and euthanasia.