The first modern taxonomic classification of the species of Lepraria is presented. Chemistry is the most important character used to separate the morphologically similar, but distinct, sterile taxa. Nine species are recorded from the British Isles, of which L. eburnea and L. frigida are new to science. Lepraria nivalis is a new name for Crocynia murorum B. de Lesd., and L. caesioalba (B. de Lesd.) Laundon a new combination. Two species, L. incana (L.) Ach. and L. lobificans Nyl., are especially common and are dominant on shaded bark and rock. Twenty-eight lichens reported as Lepraria belong elsewhere or require further study. The combination Leproloma cacuminum (Massal.) Laundon is made to replace the name L. angardianum.