The Threefold Law is a belief held by some practitioners of Wicca. According to the Threefold Law, any energy which is put out into the world will be returned at three times its strength, whether this energy is positive or negative. Essentially, the Threefold Law is about reciprocity, and a reminder to people that they should be mindful about their actions, considering things before engaging in them to think about their impact on the world.

For Wiccans who believe in the Threefold Law, this concept is included in the Wiccan Rede, which is a code of ethical content for Wiccans. The content of the Wiccan Rede varies, depending on one's personal interpretation of Wicca and Neopagan morality. Some Wiccans reject the Threefold Law, arguing that it is too closely associated with Judeo-Christian influences, while others accept it, likening it to concepts of karma and laws of return in other religious traditions.

The return of energy involved in the Threefold Law is not necessarily straightforward. If someone gives another person an orange, for example, three oranges will not magically appear the next day, but that good deed may be returned in some other way, potentially far into the future. The return is not supposed to be immediate or directly reciprocal, making the Threefold Law very similar to concepts like karma, with all of someone's actions being considered, not just a single deed.

According to the Threefold Law, a Wiccan who behaves rightly and thinks of others will benefit from this by receiving positive energy and deeds later in life. Likewise, someone who chooses to do wrong will find this wrong returned at some point in life. Some Wiccans express the Threefold Law in the phrase “as we reap, so shall we sow,” or some variant thereof, stressing the idea that life is full of cyclical events and that every action has potential consequences.

Belief in the Threefold Law does not preclude attempts to atone for acts of wrongdoing. If someone recognizes that he or she has done something harmful and wants to apologize or attempt to atone for it, he or she is encouraged to do so, and this act may also be returned in some way in the future. There is a heavy emphasis on personal responsibility in the Threefold Law, with Wiccans who believe in it focusing on the fact that their actions, no matter how small, have consequences.