Druidry is the most neglected by academia among all world faiths. White there are thousands of contemporary practitioners and a clear line of descent from the most ancient cultures of Celtic Europe, the fields of knowledge that are needed to master this discipline are so complex, so multifarious and so multidimensional, that hitherto no one has attempted to provide an overall picture of the terrain in a single Encyclopedia. This work can be likened to an aerial photographic expedition over an entire continent of knowledge. Some of it is new knowledge (eg. recent archaeological discoveries of Celtic civilization) some of it is old knowledge reconfigured (the hundreds of studies of Druidry gong right back to classical antiquity, here summarised and commented on in detail for the first time in history). This work has taken over 40 years of study to assemble into the current three volume shape. The author has spent many years serving in various capacities in the pagan, Christian and Druid worlds.