Thoth Tarot is an esoteric tarot deck painted by Lady Frieda Harris according to instructions from Aleister Crowley. Crowley referred to this deck as The Book of Thoth, and also wrote a 1944 book of that titleintended for use with the deck.

Crowley originally intended the Thoth deck to be a six-month project aimed at updating the traditional pictorial symbolism of the tarot. However, due to increased scope, the project eventually spanned five years, between 1938 and 1943

The illustrations of the deck feature symbolism based upon Crowley's incorporation of imagery from many disparate disciplines, including science and philosophy and various occult systems (as described in detail in his The Book of Thoth).

Crowley renamed several of the trumps compared to earlier arrangements, and also re-arranged the numerical, astrological and Hebrew alphabet correspondences of 4 trumps compared to the Hermetic Order of the Golden Dawn's inner order deck in accordance with the Tarot of Marseilles, his 1904 book The Book of the Law (Liber AL vel Legis) and its "New Commentary."[2] In the "New Commentary" and The Book of Thoth, Crowley demonstrates that his trump arrangement forms a double loop in the zodiac-number and letter-number correspondences compared to the Golden Dawn deck, where there is no loop.[1]

All these old letters of my Book are aright; but צ is not the Star.[3]

Tzaddi is the letter of The Emperor, the Trump IV, and He is the Star, the Trump XVII. Aquarius and Aries are therefore counterchanged, revolving on the pivot of Pisces, just as, in the Trumps VIII and XI, Leo and Libra do about Virgo. This last revelation makes our Tarot attributions sublimely, perfectly, flawlessly symmetrical.[2]

For The Star is referred to Aquarius in the Zodiac, and The Emperor to Aries. Now Aries and Aquarius are on each side of Pisces, just as Leo and Libra are on each side of Virgo; that is to say, the correction in the Book of the Law gives a perfect symmetry in the zodiacal attribution, just as if a loop were formed at one end of the ellipse to correspond exactly with the existing loop at the other end.[

Harris' renditions of the tarot are on watercolor paper affixed to a thick backing; the acidity of the backing, according to a report from 2006, resulted in discoloration of borders, and to some extent, the paintings themselves. The paintings also required cleaning and the repair of small tears.[6] A conservation plan called for cleaning the surfaces, the removal of backing (while retaining original inscriptions), reuse of the hand-painted window mats, and replacement of overlays with acid-free, museum-quality paper. The project was completed in 2011.[6] The paintings are owned by the Warburg Institute; work was completed by the Institute's in-house specialist, Susan Campion.

Aleister Crowley had asked playwright and author Clifford Bax to help him find an artist for a Tarot project. On 9 June 1937 Bax invited Frieda Harris after two artists did not show up for an appointment. She was then aged 60.

As well as reading books by Crowley, Harris' study of Rudolf Steiner's Anthroposophy was to be a critical aspect in the creation of the Thoth deck. Crowley's friend Greta Valentine, a London socialite, also knew Harris. Harris and Crowley did much of their work on the Thoth tarot deck at Valentine's house in Hyde Park Crescent, London.

In 1937 Harris began taking lessons in projective synthetic geometry, based upon the ideas of Goethe as reflected in the teachings of Steiner, from Olive Whicher and George Adams.

John Symonds writes:

[Crowley] helped her through the portals of the mystical Order of the A∴A∴ (Argenteum Astrum) She took the name of Tzaba "Hosts", which adds up to 93, the number of the Thelemic current which she was trying to tap.[3]

According to Crowley's unpublished Society of Hidden Masters,[4] on 11 May 1938, Lady Harris became his "disciple" and also became a member of Ordo Templi Orientis, entering directly to the IV° (Fourth Degree) of that Order due to her previous initiation into Co-Masonry.[5]

Crowley also began to teach her divination — she had a choice of discipline and opted for the I Ching.

By Crowley's own admission, the deck was originally intended to be traditional but Harris encouraged him to commit his occult, magical, spiritual and scientific views to the project.

Harris sent Crowley a regular stipend throughout the project. She also used her society contacts to find financial backers for the exhibition of the paintings, the catalogues, and for the publication of the Tarot deck. The pressure may have taken its toll on Harris and Crowley was sufficiently concerned to call in the lawyers to protect his 66% investment in the project. Crowley gives Harris praise in the introduction to the Book of Thoth:

She devoted her genius to the Work. With incredible rapidity she picked up the rhythm, and with inexhaustible patience submitted to the correction of the fanatical slave-driver that she had invoked, often painting the same card as many as eight times until it measured up to his Vanadium Steel yardstick![6]

Throughout the project she insisted on her own anonymity but she revelled in working for such a notorious man. The Book of Thoth was published in 1944 in a 200 copy limited edition, but neither Crowley or Harris lived to see the deck itself printed