Jan Jakob Maria de Groot (18 February 1854, Schiedam - 24 September 1921, Berlin) was a Dutch Sinologist and historian of religion. He taught at Leyden and later in 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".