Michael Horowitz is a historian, author, archivist, and bookseller working in the field of psychoactive plants and drugs. He has co-edited several topical books with his wife, Cynthia Palmer, and with Karen Walls and Billy Smith, he compiled an exhaustive annotated bibliography of Timothy Leary's works.

Horowitz first met Leary in the summer of 1970, when Leary was in prison facing ten years, plotting his escape, and worried that the government would seize his archives. Leary was therefore quite happy to turn his collected papers and books over to Horowitz and his partner Robert Barker for safekeeping, which secured Horowitz a position as Leary's archivist. Horowitz retained the materials while Leary was incarcerated and in exile during the 1970s, and he has worked to preserve and disseminate Leary's works since that time. (Over the course of their existence, Leary's archives have been taken by the FBI, the subject of a Grand Jury Investigation, eventually returned to Leary, recently digitized, and even more recently obtained by the New York Public Library.)

As an avid bibliophile and economically challenged member of the hippie counterculture, there were times when Horowitz had to make the hard decision between spending money on food and purchasing some highly desired tome that he had come across. Books often won out over bagels, and over the years Horowitz compiled an astonishing number of titles. In the same year that he met Leary, Horowitz decided to merge his own book collection with those of Robert Barker and William Dailey, in order to co-found a library named in honor of Fitz Hugh Ludlow, author of the first American book on the psychoactive drug experience, The Hasheesh Eater (1857). Along with acting as a repository, they also published some original books and reprints of classic titles. For a time, the Fitz Hugh Ludlow Memorial Library was the world's largest collection related to psychoactive plants and drugs, containing over ten thousand books and other materials. However, the library was eventually sold to Julio Mario Santo Domingo Braga, who combined it with his own collection to create the massive Ludlow-Santo Domingo (L.S.D.) Library in Geneva.

Horowitz has been a contributing editor to High Times magazine, and is currently on the Advisory Board for the Psychoactive Substances Research Collection at Purdue University Libraries. These days an ex-pat living in Canada, Horowitz continues to run Flashback Books (the mail order company he founded in 1985), which deals in rare books, periodicals, and other printed materials related to psychoactives.