Conversational encyclopaedias were considered, in the 19th century, to be a repository of social knowledge. The various encyclopaedias and encyclopaedic dictionaries provided an opportunity to acquire (new) knowledge and to negotiate social knowledge. This book takes this observation as its starting point to explore the social knowledge that may have served as the basis for the new definition of anti-Semitism formulated by Wilhelm Marr in 1879. In an initial field test, this work explores new avenues of insight for anti-Semitism research through a discourse analysis of the article 'Juden' (Jews) in the 19th-century Brockhaus encyclopaedia.