Sacred groves or sacred woods are groves of trees that have special religious importance within a particular culture. Sacred groves feature in various cultures throughout the world.

Ancient Celtic religion, commonly known as Celtic paganism, was the religion of the ancient Celtic peoples of Europe. Because there are no extant native records of their beliefs, evidence about their religion is gleaned from archaeology, Greco-Roman accounts, and literature from the early Christian period. Celtic paganism was one of a larger group of polytheistic Indo-European religions of Iron Age Europe.