encyclopedia, compendium of knowledge, either general (attempting to cover all fields) or specialized (aiming to be comprehensive in a particular field).

Encyclopedias and Other Reference Books

Basically an encyclopedia differs from a dictionary in that a dictionary is fundamentally devoted to words and an encyclopedia offers information on various subjects, with data on and discussion of each subject identified. An almanac differs from an encyclopedia in that an almanac normally is issued periodically and includes ephemeral data applicable at the time of issue, while an encyclopedia is assembled from accumulated knowledge within a broader scope. An atlas is devoted to maps and charts.

Early Encyclopedias

Attempts at encompassing universal knowledge began with the brilliantly comprehensive works of Aristotle. Other classical writers tried to follow his example, and the Natural History of Pliny the Elder is sometimes called the first encyclopedia. Alexandrian scholars did some work of an encyclopedic nature in compiling their lengthy anthologies and summations of knowledge. The Asian encyclopedias, particularly the voluminous Chinese collections, were actually more in the nature of anthologies than reference works. In the Middle Ages various scholars drew up compendiums of knowledge; notable were the Etymologiae of Isidore of Seville, a curious mixture of fact and legend, and 13th-century works by Vincent of Beauvais, Roger Bacon, and Brunetto Latini.

Modern Encyclopedias

The modern type of encyclopedia—with alphabetical arrangement and frequently with bibliographies—is usually said to have been established by John Harris in his Lexicon technicum (1704). Perhaps the most renowned of all encyclopedias, the Encyclopédie, was completed in 1772 by Diderot and others in France. The first edition of the Encyclopaedia Britannica was published in three volumes (1768-71). It grew in size and reputation over the years; despite its name, it is now published in the United States.

The oldest German encyclopedia still being published is Brockhaus' Konversations-Lexikon, first issued from 1796 to 1808. On this, rather than on Ephraim Chambers's Cyclopaedia (1st ed. 1728), was based the British Chambers's Encyclopedia (1st ed. 1859-68). The famous Larousse Grand Dictionnaire universel du XIXème siècle français in 17 volumes was published from 1865 to 1888. The 30-volume Saudi Global Arabic Encyclopedia, the first modern encyclopedia in Arabic and with an Arab perspective, was published in 1997.

The first noteworthy American encyclopedia was The Encyclopedia Americana, edited by Francis Lieber (13 vol., 1829-33). Important American encyclopedias include Collier's Encyclopedia (24 vol., 1949-51) and Encyclopedia International (20 vol., 1963). Notable multivolume juvenile encyclopedias are The Book of Knowledge (1910), World Book Encyclopedia (1917), Britannica Junior (1934), Compton's Pictured Encyclopedia (1922), and Merit Students Encyclopedia (1967).

The Encyclopaedia Britannica completely revised its format and now publishes a 30-volume edition divided into three parts: the Propaedia, a 1-volume outline of the whole; the Micropaedia, a 12-volume short-entry set; and the Macropaedia, a 17-volume long-entry set with articles by noted authors and scholars. Since the advent of computer technology, several encyclopedias have been made available in CD-ROM format (see compact disc), sometimes as part of a reference package; and as part of an on-line service. CD-ROM encyclopedias typically offer multimedia enhancements, such as video and sound clips and animated illustrations, and on-line encyclopedias especially are frequently updated. All electronic encyclopedias make use of hypertext cross-references. Another product of the computer age is the Wikipedia, an Internet-based on-line encyclopedia (est. 2001) sponsored by a non-profit corporation and written and edited collaboratively by volunteers (anyone may submit articles, additions, or corrections). By the early 2000s it had about 1.6 million entries in some 100 languages, with about 600,000 entries in English.

Some specialized encyclopedias are in many volumes, such as the Encyclopedia of Philosophy, the International Encyclopedia of the Social Sciences, the Encyclopedia of Islam, and the New Grove Dictionary of Music. Most specialized encyclopedias, however, are one volume or two. The one-volume general encyclopedia became popular in Europe early in the 20th cent., but the first comprehensive one-volume general encyclopedia in English was The Columbia Encyclopedia (1935), now in its sixth edition. A number of compact desk encyclopedias are also now available.

Reference work that contains information on all branches of knowledge or that treats a particular branch of knowledge comprehensively. It is self-contained and explains subjects in greater detail than a dictionary. It differs from an almanac in that it is not an annual publication that provides information about a particular year, and it differs from pedagogical texts in its attempt to be easy to consult and to be readily understood by the layperson. Though generally written in the form of many separate articles, encyclopaedias vary greatly in format and content. The prototype of modern encyclopaedias is usually acknowledged to be Ephraim Chambers's Cyclopaedia (1728). The first modern encyclopaedia was the French Encyclopédie (1751–65). The oldest general encyclopaedia in English is the Encyclopædia Britannica.

Learn more about encyclopaedia with a free trial on Britannica.com.