The Encyclopædia Britannica (Latin for "British Encyclopaedia"), published by Encyclopædia Britannica, Inc., is a general knowledge English-language encyclopaedia. It is written and continuously updated by about 100 full-time editors and more than 4,000 contributors, who have included 110 Nobel Prize winners and five American presidents. It is regarded as one of the most scholarly of English language encyclopaedias.

The Britannica is the oldest English-language encyclopaedia still being produced. It was first published between 1768 and 1771 in Edinburgh, Scotland 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. Beginning with the 11th edition and its acquisition by an American firm, the Britannica shortened and simplified articles to broaden its appeal in the North American market. In 1933, the Britannica became the first encyclopaedia to adopt "continuous revision", in which the encyclopaedia is continually reprinted and every article updated on a schedule. In March 2012, Encyclopædia Britannica, Inc. announced it would no longer continue to publish its printed editions, instead focusing on its online version, Encyclopædia Britannica Online. Its final print edition was in 2010, a 32-volume set.