Tijuana bibles (also known as eight-pagers, bluesies, gray-backs, Jiggs-and-Maggie books, jo-jo books, Tillie-and-Mac books, and two-by-fours) were little pornographic 8-page comic books produced and sold illegally in the United States from the 1920s to the early 1960s. Prices are based on age (originals vs. reprints), scarcity, popularity of its characters, and condition.