Written anonymously, The Cloud of Unknowing is a treatise which discusses the human soul, and how God interacts with it to form each person's spiritual journey.

A manual of prayer and God split into seventy-five short chapters, this book is intended to be read slowly, so that the author's comprehension is maximized. First written in Middle English during the 15th century, the words are archaic but made comprehensible by author Evelyn Underhill, who performed edits upon the original text in the early 20th century.

Unusually for the period, this treatise is imbued with plentiful good humor and a gentle tone. The author does not seek to preach oppressively or with threats of damnation, but instead offers readers a relaxed, thoughtful yet devoted manual of faith and advice on living a joyous, spiritually mindful life. Although the book is old, the wisdom and guidance it offers is imbued with timelessness.

Evelyn Underhill - an author who wrote extensively on the subjects of mysticism and spiritual experiences - was fascinated by this surviving work of the late Middle Ages. It was apparently written as private advice between a pupil and master, and was not intended for wide publication. Underhill explains her affinity to this text in her introduction, identifying it as a prime example of Christian mysticism, and noting past examples wherein mystics and spiritualists have influenced Christianity.