The Encyclopædia Britannica (Latin for "British Encyclopaedia") is a general knowledge English-language encyclopaedia. It is published by Encyclopædia Britannica, Inc.; the company has existed since the 18th century, although it has changed ownership various times through the centuries. The encyclopaedia is maintained by about 100 full-time editors and more than 4,000 contributors. The 2010 version of the 15th edition, which spans 32 volumes and 32,640 pages, was the last printed edition. Since 2011, it is being published exclusively as an online encyclopaedia.

Printed for 244 years, the Britannica was the longest running in-print encyclopaedia in the English language. It was first published between 1768 and 1771 in the Scottish capital of Edinburgh, as three volumes. The encyclopaedia grew in size: the second edition was 10 volumes, and by its fourth edition (1801–1810) it had expanded to 20 volumes. Its rising stature as a scholarly work helped recruit eminent contributors, and the 9th (1875–1889) and 11th editions (1911) are landmark encyclopaedias for scholarship and literary style. Starting with the 11th edition and following its acquisition by an American firm, the Britannica shortened and simplified articles to broaden its appeal to the North American market. In 1933, the Britannica became the first encyclopaedia to adopt "continuous revision", in which the encyclopaedia is continually reprinted, with every article updated on a schedule. In March 2012, Encyclopædia Britannica, Inc. announced it would no longer publish printed editions and would focus instead on the online version.

In the third era (10th–14th editions, 1901–1973), the Britannica was managed by American businessmen who introduced direct marketing and door-to-door sales. The American owners gradually simplified articles, making them less scholarly for a mass market. The 10th edition was an eleven-volume supplement (including one each of maps and an index) to the 9th, numbered as volumes 25–35, but the 11th edition was a completely new work, and is still praised for excellence; its owner, Horace Hooper, lavished enormous effort on its perfection.

См. также: Енциклопедія сучасної України, Википедия, Большая российская энциклопедия