The Irish words, pronounced "arn ree-ocht fane", mean "Our Own Druidism". The ADF is an independent tradition of neopagan druidism. They, like most other neopagan faiths, are attempting to revive the best aspects of paleopagan faiths in a modern context.
The ADF is focused on research and sound scholarship about the ancient Celts and other Indo-European people. Their focus is on the sort of generalized ancient European pagan religions, rather than just the Celtic facet, welcoming Norse, Hellenic, Baltic, Slavic, and Latin pagans. Their mottos are "Why not excellence?" indicating that they intend to focus on solid foundations, and "As fast as a speeding oak tree!" pointing out that excellence takes time.
Ar nDraiocht Fein was founded in 1983 after Isaac Bonewits wrote an "Open Letter" wanting to bring organization and scale to the scattered neopagan movement. It started off as largely a scholarly exchange that turned into its own tradition. It is considered an offshoot of the Reformed Druids of North America. Major focuses have included the development of a cohesive clergy training program, which is intended to bring neopagan clergy up to the standards of mainstream religion by including training in group dynamics, counseling, conflict resolution, and other important areas besides the spiritual/magical side of religion. They aim to mainstream both neopaganism into the mainstream and with it, themselves..
The ADF has both solitary and grove members. An interesting facet of their organization is that they are required to hold their celebrations in public parks or other places where anyone can join in. Membership is, however, open to everyone, being linked more with their scholarly side than their religious sie. They are managed by a board of directors referred to as the Mothergrove, with a head Archdruid. There are three circles to their organization; First Circle is just about all members, Second Circle is those interested in local leadership/starting a grove, and Third Circle is those wanting to lead/help the organization as a whole.
They celebrate the eight High Days of the Druidic Calendar, though the names given may vary with the origin of the pantheon a particular grove focuses on. Their overall focus is polytheistic, without a Supreme Evil, and with a focus on nature.
The Henge of Keltria sprung from the ADF, just as (in a way) the ADF sprung from the Reformed Druids of North America.
For more information, their comprehensive official website may be found at http://www.adf.org/.