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 4,400 contributors. 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 (1801–1809) it had expanded to 20 volumes. Its rising stature helped recruit eminent contributors, and the 9th edition (1875–1889) and the 11th edition (1911) are landmark encyclopaedias for scholarship and literary style. Beginning with the 11th edition, 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.

The 15th edition has a three-part structure: a 12-volume Micropædia of short articles (generally fewer than 750 words), a 17-volume Macropædia of long articles (two to 310 pages) and a single Propædia volume to give a hierarchical outline of knowledge. The Micropædia is meant for quick fact-checking and as a guide to the Macropædia; readers are advised to study the Propædia outline to understand a subject's context and to find more detailed articles. The size of the Britannica has remained roughly constant over 70 years, with about 40 million words on half a million topics. Although publication has been based in the United States since 1901, the Britannica has maintained British spelling.