Ogham is an Early Medieval script used predominately to write in the Old Irish and Brythonic languages. It is sometimes known as the “Celtic Tree Alphabet”, based on a high medieval Bríatharogam tradition ascribing names of trees to the individual letters of the alphabet. There are around 400 known, surviving ogham inscriptions on stone monuments throughout Ireland and western Britain. Most of them are in southern Ireland, in Counties Kerry, Cork and Waterford. The largest number outside of Ireland is in Pembrokeshire in Wales. The remainder are mostly in south-eastern Ireland, Scotland, Orkney Isles, the Isle of Man, and England around the Devon/Cornwall border. Most of the inscriptions are of personal names.
The main use of ogham by modern Druids and Pagans is for divination purposes. Divination by using ogham symbols is mentioned in Tochmarc Étaíne, a tale in the Irish Mythological Cycle. In the story, druid Dalan takes four wands of yew, and writes ogham letters upon them. Then he uses the tools for divination.The tale doesn’t explain further how the sticks are handled or interpreted. Another method requires a cloth marked out with Finn’s Window. A person selects some sticks randomly, throws them on the cloth, and then looks both at the symbols and where they fell.
The divinatory meanings are usually based on the tree ogham, rather than the kennings of the Bríatharogam. Each letter is associated with a tree or other plant, and meanings are derived from them. Robert Graves’ book The White Goddess has been a major influence on assigning divinatory meanings for ogham. Some reconstructionists of Druidic ways use Briatharogam kennings as a basis for divinatory meanings in ogham divination. The three sets of kennings can be separated into Past-Present-Future or Land-Sea-Sky groupings in such systems, but other organizing structures are used, as well.