The triquetra is often found in Insular art, most notably metal work and in illuminated manuscripts like the Book of Kells. It is also found in similar artwork on Celtic crosses and slabs from the early Christian period. The fact that the triquetra rarely stood alone in medieval Celtic art has cast reasonable doubt on its use as a primary symbol of belief. In manuscripts it was used primarily as a space filler or ornament in much more complex compositions, and in knotwork panels it is a design motif integrated with other design elements. Celtic art lives on as both a living folk art tradition and through several revivals. This widely recognized knot has been used as a singular symbol for the past two centuries by Celtic Christians, Pagans and agnostics as a sign of special things and persons that are threefold.
Due to its presence in insular Celtic art, Celtic Reconstructionists use the triquetra either to represent one of the various triplicities in their cosmology and theology (such as the tripartite division of the world into the realms of Land, Sea and Sky), or as a symbol of one of the specific triple Goddesses, for example, The Morrígan.
It is difficult to date the exact origin of the Celtic triquetra, and whether it was first used in a Christian or pagan context; the distinctive interlace/knotwork artistic style did not fully develop until ca. the 7th century A.D., but the triquetra is the simplest possible knot. Modern Pagans use the triquetra to symbolize a variety of concepts and mythological figures.
Germanic Neopagan groups who use the triquetra to symbolize their faith generally believe it is originally of Norse and Germanic origins.
The symbol is also sometimes used by wiccans and some New Agers to symbolize the Triple Goddess, or as a protective symbol.