Published since 1917, the World Book Encyclopedia is a general reference work. The encyclopedia deliberately uses nontechnical language and abundant graphics to make it especially accessible to students and general readers without sacrificing depth and accuracy. The editors of the first edition emphasized the use of "everyday, simple language" in the eight-volume set.

In 1919, World Book began the practice of printing annual revisions of its encyclopedia, which has been followed every year since except for 1920, 1924, and 1932. World Book's first major revision took place in 1929, when the set was expanded to thirteen volumes. In 1931, World Book adopted the unit-letter system of arrangement, in which each volume was a different-sized book that contained all the entries for one or more letters of the alphabet. The set was expanded to nineteen volumes in 1933, to twenty volumes in 1960, and to twenty-two volumes in 1972. The final volume in the...