Worl Book Encyclopedia is, according to its publisher in the United States, "the number-one selling print encyclopedia in the world." It is based in Chicago, Illinois. The first edition (1917) contained eight volumes. New editions have since appeared every year except 1920, 1924, and 1932, with major revisions in 1930 (13 volumes), 1947 (18,000 illustrations), 1960 (20 volumes), and 1988.