
National Book Month was established by the National Book Foundation, the organization also responsible for the prestigious National Book Awards. While the exact year of inception for the month-long celebration isn't always clearly cited, the Foundation itself has been promoting books and reading since its re-establishment in 1988 (it has earlier roots dating back to the 1950s).
The month serves as an extended platform to amplify the Foundation's mission: "to celebrate the best literature in America, expand its audience, and ensure that books have a prominent place in American culture." October was likely chosen as it leads up to the National Book Awards ceremony, typically held in November.