The "Three Initiates" who authored The Kybalion chose to remain anonymous.
As a result, a great deal of speculation has been made about who actually wrote the book. The most common proposal is that The Kybalion was authored by William Walker Atkinson, either alone or with others, such as Paul Foster Case and Elias Gewurz.
Atkinson was known to use many pseudonyms, and to self-publish his works. Also suggestive is that among his earliest published pseudonymous and anonymous works may have been a series entitled The Arcane Teachings (first published prior to 1909 and the second edition in 1909), which bears many superficial similarities to The Kybalion. While the latter explores seven "Hermetic Principles", The Arcane Teachings examines seven "Arcane Laws";
The Kybalion claims to be an elucidation of an ancient, unpublished Hermetic text of the same name, and The Arcane Teachings claims to reveal the wisdom of an ancient, unpublished scroll of occult aphorisms.
Both books describe three "Great Planes" of reality which are further subdivided into seven lesser planes.
Both also describe three of the lesser planes as "astral black keys" analogous to the black keys on a piano, and inhabited by elemental spirits.
And both books describe the process of "Mental Alchemy" in great detail, and in near-complete agreement with each other. There are other similarities, and some argue that
The Arcane Teachings might have been Atkinson's "first draft" of material which later became The Kybalion. Atkinson also attempted to describe the workings of the universe in terms of a set of laws in his last manuscript The Seven Cosmic Laws, written in 1931 and published posthumously in 2011.
A common theory is that Atkinson co-wrote the book with Paul Foster Case and Michael Whitty. This theory is often held by members of Builders of the Adytum (B.O.T.A.), the Mystery School later founded by Case, though it doesn't publicly make this claim. This story appears to have originated with a B.O.T.A. splinter group, the Fraternity of the Hidden Light. Along these lines, much has been made about Paul Foster Case's being a Freemason, and that The Kybalion's publisher, the Yogi Publication Society, gave its address as "Masonic Temple, Chicago IL" on the book's frontispiece.
However, Chicago's "Masonic Temple" was also the city's first skyscraper, housing dozens of stores and small businesses without any Masonic affiliations, and named for the Masonic Lodge which financed much of its construction and met in its top few floors.
Other names speculatively mentioned as co-authors of The Kybalion include Harriet Case (Paul Foster Case's wife at the time), Mabel Collins (a prominent Theosophical writer), Claude Bragdon (an architect, Theosophist, and writer on "mystic geometry"), and Claude Alexander (a well-known stage magician, mentalist, proponent of crystal gazing, and New Thought author).
Ann Davies, who succeeded Case as head of the B.O.T.A., is often mentioned as a possible Kybalion contributor, but she was born in 1912—four years after the book's first publication.
The introduction for a 2011 edition of The Kybalion published by Tarcher/Penguin presents an argument that William Walker Atkinson was the sole author of the work, including evidence such as the 1912 edition of Who's Who in America, which attributes Atkinson as the author, and a 1917 French language edition of The Kybalion in which the translator's introduction attributes the work to "the American psychic master W.W. Atkinson."