Since the publication of the comprehensive account of the British desmid flora contained in the five volumes of the British Desmidiaceae (W. & G.S. West 1904, 1905, 1908, 1912 and W. & G.S. West and Carter 1923) no subsequent check-list las been produced of these exclusively freshwater algae. Several researchers, not only in Britain but from elsewhere have expressed an interest in such a list. Being currently engaged in a complete revision of the West's classic volumes, and having added numerous new records to the British desmid flora from extensive collecting undertaken over many years from diverse regions of the British Isles, the authors have prepared this check-list.