Chicago Mobs of the Twenties was a reference book, written by Billings and Torgelson (TOS novel: Starfleet: Year One) and released by book publishers Simon and Schuster in November 1992 (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 2) The book was a history of the mob in the Earth city of Chicago during the 1920s.

Two different starships named Horizon have been said to have left Chicago Mobs of the Twenties behind on Sigma Iotia II.

ECS Horizon crewman Nora Melchior kept a hardcopy on a shelf in her quarters, when friend Travis Mayweather spoke to her, in private. (ENT episode: "Horizon") When the Horizon visited Sigma Iotia II in 2155, the book was traded to the Iotians by the ship's crew. (ENT novel: Kobayashi Maru)

Chicago Mobs of the Twenties was a reference work used by the USS Horizon first contact team when they visited Sigma Iotia II in 2168. However, they left their copy behind when they broke orbit (ST reference: The Worlds of the Federation, Decipher RPG module: Worlds).

The Iotians viewed the society depicted in the book as ideal, and rebuilt their own accordingly, quickly adopting "the Book" as it became known as something of a cultural bible (TOS episode: "A Piece of the Action"; ENT novel: Kobayashi Maru)

Simon and Schuster is the parent company of Pocket Books, the licensee for Star Trek fiction from 1979 onwards.