The Letters O.T.O. stand for Ordo Templi Orientis, the Order of Oriental Templars, or Order of the Temple of the East. O.T.O. is an Outer Thelemic Order which is dedicated to the high purpose of securing the Liberty of the Individual and his or her advancement in Light, Wisdom, Understanding, Knowledge, and Power through Beauty, Courage, and Wit, on the Foundation of Universal Brotherhood.

O.T.O. is the first of the great Old Æon orders to accept The Book of the Law, received by Aleister Crowley in 1904 E.V. This book proclaims a New Æon in human thought, culture and religion. The Æon arises from a single supreme injunction: the Law of Thelema, which is Do what thou wilt. This is not to be interpreted as a license to indulge every passing whim, but rather as the divine mandate to discover one's True Will or true purpose in life, and to accomplish it; leaving others to do the same in their own unique ways.

The methods and practices to be employed in this process are numerous and varied, and are grouped together under the generalized term "Magick". Any action which is not directed toward the discovery and accomplishment of the True Will is considered to be malignant and "black magic". This includes acts of interference with any other individual's lawful exercise of their right to discover and accomplish their own True Will.

O.T.O. also includes a specifically liturgical arm, Ecclesia Gnostica Catholica (E.G.C.), or the Gnostic Catholic Church, the principal ritual of which is the Gnostic Mass. E.G.C. also celebrates seasonal festivals, commemoration of vital events and other religious functions. Membership in E.G.C. is available through baptism and confirmation. Members of O.T.O. in good standing are eligible for clerical ordination in E.G.C. Many O.T.O. local bodies celebrate the Gnostic Mass on a regular basis, and in most locations, no formal affiliation is required to attend the Mass.

O.T.O. has long worked in close alliance with the A∴A∴, which first proclaimed the Law of Thelema to the world. The A∴A∴ is a teaching and initiatory structure dedicated to the personal spiritual advancement of its individual members. Within A∴A∴ all services are rendered free of charge, and no social activities are held. Although distinctly separate organizations, O.T.O. has historically assisted A∴ A∴ with practical matters that lie outside its primary mission, which is purely spiritual in nature.

O.T.O. currently operates in twenty different countries around the world with over 4,000 active members. Within the broad context of Thelema, O.T.O. functions as a fraternal, initiatory, social, and educational organization of a religious nature.