The World Book Encyclopedia is an American encyclopedia. World Book was first published in 1917. Since 1925, a new edition of the encyclopedia has been published annually. Although published online in digital form for a number of years, World Book is currently the only American encyclopedia which also still provides a print edition. The encyclopedia is designed to cover major areas of knowledge uniformly, but it shows particular strength in scientific, technical, historical and medical subjects.

An encyclopedia or encyclopaedia is a reference work or compendium providing summaries of knowledge, either general or special, in a particular field or discipline. Encyclopedias are divided into articles or entries that are arranged alphabetically by article name or by thematic categories, or else are hyperlinked and searchable. Encyclopedia entries are longer and more detailed than those in most dictionaries. Generally speaking, encyclopedia articles focus on factual information concerning the subject named in the article's title; this is unlike dictionary entries, which focus on linguistic information about words, such as their etymology, meaning, pronunciation, use, and grammatical forms.