Collier's Encyclopedia (full title: Collier's Encyclopedia with Bibliography and Index) was a United States-based general encyclopedia published by Crowell, Collier and Macmillan. Self-described in its preface as "a scholarly, systematic, continuously revised summary of the knowledge that is most significant to mankind", it was long considered one of the three major contemporary English-language general encyclopedias, together with Encyclopedia Americana and Encyclopædia Britannica: the three were sometimes collectively called "the ABCs".
P.F. Collier & Son Company published Collier's New Encyclopedia from 1902–1929, initially in 16 volumes and later in 10 volumes.
Collier's 11 volume National Encyclopedia (1932–1950) replaced Collier's New Encyclopedia.
In 1949 the entirely new 20 volume Collier's Encyclopedia replaced the National Encyclopedia.
After Robert Collier's death in 1918, P.F. Collier & Son Company was bought by Crowell Publishing Company (later the Crowell-Collier Publishing Company). In 1950 Crowell, Collier and Macmillan published the 20 volume Collier's Encyclopedia (full title Collier's Encyclopedia with Bibliography and Index). It was expanded to 24 volumes in 1962. Until its print edition ceased in 1998, Collier's Encyclopedia was sold almost exclusively door-to-door, one of the last big-ticket items of that nature in the United States.
The 1997 edition has 23,000 entries with few short entries, as related subjects are usually consolidated into longer articles. A high percentage of the illustrations are in color, and more full-color illustrations had been added in recent years resulting in pictorial matter accounting for about two-fifths of the pages. Bibliographies are found in the last volume which also contains the 450,000 entry essential index. An annual Collier's Year Book was also published.
In 1998 Microsoft bought the rights to Collier's electronic version and incorporated it into its Encarta electronic encyclopedia. Atlas Editions (formerly Collier Newfield) retained the rights to publish the encyclopedia in book form, though since then, Collier's has ceased to be in print.