F. C. Happold (1893–1971)

This is not the definitive work on Mysticism. (I'm not sure that has even been written). It is, however, the best introduction to the subject in the English language. A work of two halves - a Study followed by an Anthology - it includes all the major strands of Christian mysticism plus discussions of Buddhism, Hinduism, Sufism, Platonic thought, and a few expressions from the lives of quite ordinary people who experienced one of those 'timeless moments'.
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Happold concentrates unequivocally on the Christian mystics, for which he makes no apology, which does however tend to skew the novice reader's mind towards the (incorrect) assumption that Christianity is the principle religion for mystical experience. That said, it is an excellent study, a superb selection of writings, and ultimately brings to the fore some Christian mystics who may be otherwise unfamiliar to even quite knowledgeable and committed Christians. A must-read for anyone wishing to know about mysticism (though not in any sense a manual for anyone wishing to start on a mystical path of experience, nor does it claim to be).… (more)

FRom the back of the book:

In this clear, simple and illuminating book, the author combines a study of mysticism - as experience, as spiritual knowledge and as a way of life - with an illustrative anthology of mystical writings. Drawing material from all over the world, the anthology includes not only selections from Christian mystics, but also from the Upanishads and the Bhagavad Gita, from Plato and Plotinus, from the Sufi mystics of Islam, from Dante and from the nature mystic, Richard Jefferies,… (more)