William Butler Yeats
Yeats, a key figure in the Celtic literary revival at the turn of the 20th Century, also moved in occult circles and knew many of the key figures of the Golden Dawn. He served as a Senator of the Irish free state and won the Nobel prize for literature in 1923.
Fairy and Folk Tales of the
Edited and Selected by W. B. Yeats 
by W. B. Yeats [1902 edition]
This is a collection of essays by Yeats on supernatural Celtic themes.
In The Seven Woods
by W. B. Yeats 
This is a short book of poetry and a play by Yeats on Irish mythological themes.
Preface to Cuchulain of Muirthemne, by Lady Gregory 
Preface to Gods and Fighting Men, by Lady Gregory 
Introduction to Gitanjali, by Rabindranath Tagore 
Notes to Visions and Beliefs in the West of Ireland, by Lady Gregory 
Witches and Wizards and Irish Folk-Lore, in Visions and Beliefs in the West of Ireland, by Lady Gregory 
Swedenborg, Mediums and the Desolate Places, in Visions and Beliefs in the West of Ireland, by Lady Gregory