An encyclopedia (or encyclopædia, cyclopædia, encyclopaedia) is a collection (usually a book) of information. Some are called "encyclopedic dictionaries".
All encyclopedias were printed, until the late 20th century when some were on CD-ROM. 21st century encyclopedias are mostly online by Internet. The largest encyclopedia in the English language is English Wikipedia, which has more than 5 million articles. The second largest is the Encyclopaedia Britannica, which is the largest one that is printed. Some languages have a larger printed encyclopedia and some have none. Either kind of encyclopedia can inform us on many different topics.
Book series intended to summarize all knowledge have been published for thousands of years. A famous early one was the Natural History by Pliny the Elder. The name "encyclopedia" is from the 16th century and meant "complete knowledge". The French Encyclopédie of Denis Diderot was the first that had major parts written by many different people.
After the printing press was invented, dictionaries with long definitions began to be called encyclopedias. For example, a dictionary of science, if it included essays, was thought of as an encyclopedia or knowledgeable book on the subject of science. Some encyclopedias then put essays on more than one subject in alphabetical order instead of grouping them together by subject. The word, encyclopedia, was put in the title of some encyclopedias.
Companies were started for the purpose of publishing encyclopedias for the public use in libraries, which is different from when an encyclopedia was the curriculum of a private school. Like dictionaries, these publishers hired hundreds of experts to write articles and read and choose articles. Some internet encyclopedias allowed their paying customers to submit articles. Other internet encyclopedias accepted writing from non-paying users of the encyclopedia. 
Types of encyclopediasEdit
There are different types of encyclopedias. Some are general and have pages on lots of topics. The English language Encyclopædia Britannica and German Brockhaus are general encyclopedias. Some are about specific topics. For example, there are encyclopedias of medicine or philosophy. Others include the Dictionary of National Biography, the Dictionary of American Naval Fighting Ships, and Black's Law Dictionary. There are also encyclopedias that that cover many topics with one perspective or one cultural bias. The Great Soviet Encyclopedia is one of these.
There are two main ways of organizing printed encyclopedias: from A to Z (the alphabetical way) or by categories. Most encyclopedias go from A to Z.
Many dictionaries have similar information to encyclopedias.
- The Compact Edition of the Oxford English Dictionary, Volume I A-O. 1971. Encyclopedia. New York: Oxford University Press.
- Webster’s Third New International Dictionary . . . Unabridged . . . Merriam-Webster. 1961. Encyclopedia. Springfield, MA: G & C Merriam Company.
- Funk & Wagnalls New Encyclopedia, Volume 9. MCMLXXXIII. Encyclopedia. USA: Funk & Wagnalls, Inc.
- The Columbia Encyclopedia in one volume. 1940. Encyclopedia. New York, NY: Columbia University Press.
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