Druidism must be understood in the context of the culture that created it. Only the Celtic people called their religious professionals Druids; other cultures had other names for their clergy, and expected different duties from them. Druids were not an ethnic or cultural group in themselves, but part of a larger society in which they participated. In the pre-christian era of Celtic culture, the Druids were members of a professional class in their culture, the Celtic Nations of Western Europe and the British Isles.

Druids filled the roles of judge, doctor, diviner, mage, mystic, and clerical scholar; in other words, they were the religious intelligentsia of their culture. To become a Druid, students assembled in large groups for instruction and training, for a period of up to twenty years. The mythologies describe Druids who were capable of many magical powers such as divination & prophesy, control of the weather, healing, levitation, and shape changing themselves into the forms of animals. Their education was so rigorous that at the end of it they were virtually walking encyclopedias. A good word for them would seem to be "priests", yet I am reluctant to use it for two reasons: The Romans never used it, and because Druids didn't minister to congregations as priests do.

Rather, they had a clientele, like a lawyer, a consultant, a mystic, or a shaman would have. Caesar and his historians never referred to them as priests, but perhaps they could not recognize them as priests since the Roman priesthood, officiating over an essentially political religion, were primarily teachers and judges, with less emphasis on being seers or diviners, whereas the Druids appeared to have both legal and magical powers and responsibilities.

A Druid's connection to nature is the source of all her powers, both in society and in magic. By understanding that connection, a Druid's being is joined with nature, and so she becomes aware of all that is known to nature, which is all things. A Druid then is a kind of nature mystic. To experience Druidism, turn off the computer and go into the woods, and listen. The voice of the old Gods are not silent. Their language is the blowing wind and the waves of the great pouring sea.

The earliest account of the Druids coincides with the beginning of the Celtic Iron Age or, La Tène period which dates from the fifth century BC to the Roman occupation of Britain and continental Europe in the first centuries, BC and AD. Among the most famous classical observers of the Druids in ancient Celtic history was Julius Caesar whose manuscripts, The Gallic Wars and The Conquest of Gaul, date to between 50 and 60 BC, the latter end of the La Tène period. In fact, the earliest commentators to write about the Druids were from the Greek and Roman world and most of their accounts date to the first century BC. The most informative commentators to write about the Druids were Julius Caesar, Strabo, and Diodorus Siculus. These writers drew from the earliest known references made by Posidonius, a Greek philosopher from Syria who wrote during the early first century BC, and Timaeus, a Greek historian who lived between the mid-fourth and mid-third centuries, BC. Timaeus's mentions of the Druids specifically are the earliest known to us. Pre-dating these writers are even earlier mentions of a noble and priestly class in Indo-European society made in the sixth century BC by the Greek writer Hecataeus of Miletus, and in the fifth century BC by the great historian Herodotus, although neither mentions the Druids specifically.

By the first century AD, the writings of Tacitus, Pliny, and Pomponius, seem to suggest that Druidism was in decline, at least in Britain, as it was a target of persecution both in Britain and in Gaul. According to the writings of Suetoniusm, Tacitus, and Pliny, the Roman emperors of the first century strongly disfavored, and attempted to suppress Druidism. Tiberius is said to have wanted the Druids eradicated because they possessed strong nationalistic ideals and influence in Gaul and were opposed to imperialism. While there are conflicting accounts by such commentators as Pliny and Suetonius, it is evident that the British Druids were a focus of Celtic nationalism, which is frequently cited as chief among the reasons Rome sought to conquer Britain.

Though accounts of the Druids virtually disappear after the first century AD, and the last such accounts speak of their persecution in Britain, it seems evident that at least until the third century, Druids apparently did continue to exist and practice their crafts in Ireland and in Gaul. No more literary references to the Druids in Britain and Gaul appear after the beginning of the fifth century however, a new written tradition was appearing in Ireland, allegedly brought by Christian monks, and which is full of allusions to Irish Druids. It was from the fifth through seventh century to the High Middle Ages that much if not the greatest majority of the mythic texts from which are drawn today's interpretations of Druid philosophy appear to have been written. Manuscripts such as the such as the seventh century Lives of St. Brigit and St. Patrick describe the period of interface between Paganism and early Christianity, during which the Druids are described as having been either accepting of, or hostile toward the new religion.

There is evidence to support that as early Christian conversion advanced across the Roman governed and Celtic lands sometime before 1500 AD, the traditionally provincial roles of the Druids and the Bards were inherited by a class of seers, teachers, poets and political advisors which came to thrive in Ireland, known as the Filidh, until about the seventeenth century, when Ireland became subject to the English crown. It was through the writings of the Filidh, though cryptic, and the early Irish mythological texts such as the Ulster Cycle and the Mythological Cycle, that knowledge of Druidic practices and beliefs were preserved, if only in part. These texts were compiled in written form sometime between the seventh and the twelfth centuries AD, and contain such epics as the Tain and the Mabinogion, and which are believed to have been passed down through much earlier oral traditions.