The Encyclopædia Britannica Eleventh Edition (1910–11) is a 29-volume reference work, an edition of the Encyclopædia Britannica. It was developed during the encyclopaedia's transition from a British to an American publication. Some of its articles were written by the best-known scholars of the time. This edition of the encyclopedia is now in the public domain, but the outdated nature of some of its content makes its use as a source for modern scholarship problematic. Some articles have special value and interest to modern scholars as cultural artifacts of the 19th and early 20th centuries. Tens of thousands of its articles were copied directly into , where they still can be found.
The 1911 eleventh edition was assembled with the management of American publisher Horace Everett Hooper. Hugh Chisholm, who had edited the previous edition, was appointed editor in chief, with Walter Alison Phillips as his principal assistant editor.
Originally, Hooper bought the rights to the 25-volume 9th edition and persuaded the British newspaper The Times to issue its reprint, with eleven additional volumes (35 volumes total) as the tenth edition, which was published in 1902. Hooper's association with The Times ceased in 1909, and he negotiated with the Cambridge University Press to publish the 29-volume eleventh edition. Though it is generally perceived as a quintessentially British work, the eleventh edition had substantial American influences, not only in the increased amount of American and Canadian content, but also in the efforts made to make it more popular. American marketing methods also assisted sales. Some 11% of the contributors were American, and a New York office was established to manage that part of the enterprise.
The initials of the encyclopedia's contributors appear at the end of selected articles or at the end of a section in the case of longer articles, such as that on China, and a key is given in each volume to these initials. Some articles were written by the best-known scholars of the time, such as Edmund Gosse, J. B. Bury, Algernon Charles Swinburne, John Muir, Peter Kropotkin, T. H. Huxley, James Hopwood Jeans and William Michael Rossetti. Among the then lesser-known contributors were some who would later become distinguished, such as Ernest Rutherford and Bertrand Russell. Many articles were carried over from the 9th edition, some with minimal updating. Some of the book-length articles were divided into smaller parts for easier reference, yet others much abridged. The best-known authors generally contributed only a single article or part of an article. Most of the work was done by journalists, British Museum scholars and other scholars. The 1911 edition was the first edition of the Encyclopædia to include more than just a handful of female contributors, with 34 women contributing articles to the edition.