While Reiki is spiritual in nature, it is not a religion. It has no dogma, and there is nothing you must believe in order to learn and use Reiki. In fact, Reiki is not dependent on belief at all and will work whether you believe in it or not. Because Reiki comes from God, many people find that using Reiki puts them more in touch with the experience of their religion rather than having only an intellectual concept of it.
While Reiki is not a religion, for optimum well being in the light of Eastern medical theory that we are a mind-body-spirit unity, it is necessary to live and act in a way that promotes harmony with others. Dr. Mikao Usui, the founder of the Reiki system of natural healing, recommended that one practice certain simple ethical ideals to promote peace and harmony, which are nearly universal across all cultures.
~International Center for Reiki Training