Medium's Blue Book

The Medium's Blue Book refers broadly to any catalogues of biographical information about frequent séance sitters and other clientele of professional mediums and allied prognosticators, also referred to as test books or pony books, that were supposed to have been compiled and traded by certain practitioners and unions in the psychic market, such as the Brotherhood of Mediums, during their heydays in the late nineteenth and early twentieth centuries.

Will Irwin, writing for Colliers in 1907, reported that there was a short-lived agency in Chicago devoted to this kind of intelligence exchange within the United States, and that many local unions maintained their own blue books, in the form of card index systems or simply traded leaflets.