Jan Jakob Maria de Groot was a Dutch sinologist and historian of religion. He taught at the Leiden University and later at the University of Berlin, and is chiefly remembered for his monumental work, The Religious System of China, Its Ancient Forms, Evolution, History and Present Aspect, Manners, Customs and Social Institutions Connected Therewith. The two "books" of this detailed and well-illustrated treatise appeared in six volumes - and, according to the preface in the first volume, the System was originally meant to include several more "books".