Detlev Clüver (1645-1708) was among the first to criticize Leibniz’s new infinitesimal analysis. Although his criticisms were vague and his methods inconsistent, Leibniz had always for him a friendly sort of consideration. The article presents Clüver’s biography, writings, and thought, together with a detailed description of Leibniz’s relations to him and of their correspondence, and contains a bibliography of Clüver’s writings.