The Book of Dzyan (comprising the Stanzas of Dzyan) is a reputedly ancient text of Tibetan origin. The Stanzas formed the basis for The Secret Doctrine (1888), one of the foundational works of the theosophical movement, by Helena Petrovna Blavatsky.
Madame Blavatsky claimed to have seen a manuscript of the Book of Dzyan while studying esoteric lore in Tibet. She claimed this and other ancient manuscripts were safeguarded from profane eyes by the initiates of an Occult Brotherhood. The work had originally, according to Blavatsky, been written in the sacred language of Senzar. She wrote 
Others have been skeptical. Max Müller is reported to have said that ‘in this matter she was either a remarkable forger or that she has made the most valuable gift to archeological research in the Orient.’
In other references Blavatsky claimed the Book of Dzyan belonged to a group of Tibetan esoteric writings known as the Books of Kiu-Te. Blavatsky wrote before a standard transcription of Tibetan into the Latin alphabet had been agreed upon; it took David Reigle some time to establish that she was referring to what modern scholars write as rGyud-sde (gyü de, section of tantras) parts of a voluminous Buddhist corpus commonly referred to as the Tantras.
Other researchers have suggested a source in Chinese Taoism or Jewish Kabbalah.
In Isis Unveiled Blavatsky herself identifies Senzar as being "ancient Sanskrit" (Isis, I, 440). As noted by John Algeo in his book, Blavatsky's other statements about Senzar (including the above linkage to Sanskrit) create a number of puzzles, which make it difficult to take the etymological language family references literally, since some link to Egyptian sources, while yet others are still of other roots.
Supposed verses from the same Stanzas of Dzyan were later published by Alice Bailey in A Treatise on Cosmic Fire in 1925. Bailey claimed these verses had been dictated to her telepathically by the Tibetan Master Djwal Kul.
Ufologist Desmond Leslie drew heavily on the Stanzas of Dzyan in his writing, and theorized that they had originally been produced on the lost continent of Atlantis.
Swiss author Erich von Däniken claimed to have explored some of the book's content and its alleged history, reporting unsourced rumours that the first version of the book predates Earth, and that chosen people who simply touch the book will receive visions of what it describes.
References to the Stanzas exist in the fiction of H. P. Lovecraft, for example in his short story "The Haunter of the Dark", and have been expanded upon by other writers who have worked within the Cthulhu Mythos.
When The Secret Doctrine appeared, William Emmette Coleman was “outraged by Madame Blavatksy’s pretensions of Oriental learning, [and] undertook a complete exegesis of her works." He claimed that her main sources were H.H. Wilson's translations of the Vishnu Purana; Alexander Winchell’s World Life: or, Contemporary Geology; Ignatius Donnely’s Atlantis (1882); and other contemporary scientific and occult works, plagiarized without credit and, in his own opinion, used in a blundering manner that showed superficial acquaintance with the subjects under discussion. He further claimed that she took at least part of her Stanzas of Dzyan from the Hymn of Creation in the old Sanskrit Rig-Veda. Coleman promised a book that would expose all of H.P.B.’s sources including that of the word Dzyan.
Historian Ronald H. Fritze notes that:
[Blavatsky] claimed to have received her information during trances in which the Masters of Mahatmas of Tibet communicated with her and allowed her to read from the ancient Book of Dzyan. The Book of Dzyan was supposedly composed in Atlantis using the lost language of Senzar but the difficulty is that no scholar of ancient languages in the 1880s or since has encountered the slightest passing reference to the Book of Dzyan or the Senzar language.
In her biography HPB: The Extraordinary Life and Influence of Helena Blavatsky, Sylvia Cranston tackles the claim of plagiarism that was leveled by William Emmette Coleman. Her view, like Coleman's, is that HPB's plagiarism consisted of quoting primary sources, without acknowledging the secondary sources from which they came.
Cranston states that a research assistant of hers took on the task of finding Coleman's alleged 70 passages that HPB plagiarized from World-Life, and could only find 6. Coleman himself, far from being an authority on occult material, was a clerk in the Quartermaster Department of the US Army. He was likely not an impartial judge, having written to Coues on July 8, 1890, "I emphatically denounced and ridiculed the theory of occultism, of elementary spirits, etc., before the Theosophical Society was organized [in 1875], and from that time to this I have strenuously opposed Theosophy all the time." Coleman promised to publish a book that would "prove" his charges against Blavatsky regarding the Book of Dzyan; this book and its proof never appeared. The reason Coleman's book never appeared is that “Coleman lost his library and his notes in the 1906 San Francisco earthquake and died three years later, his book unwritten”.