Abstract A description is provided for Puccinia striiformis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On cereals Hordeum vulgare, Secale cereale, Triticum vulgare and on over 40 genera of wild grasses including species of Agropyron, Brachypodium, Bromus and Elymus . DISEASE: Usually known as yellow rust in Europe because of its bright yellow uredia. In N. America it is known as stripe or glume rust because of the arrangement of the uredia on the leaves or glumes. GEOGRAPHICAL DISTRIBUTION: Widespread in Europe; Asia (Central, Eastern and Western and to some extent South Eastern); North America (Mid West and West Coast of Canada and USA); Central and South America, Central Africa and Malagasy Republic, apparently absent from Australasia (CMI Map 97, ed. 3, 1971). TRANSMISSION: No aecial stage is known and abundant evidence occurs of overwintering on the host plant or, with some races, on wild grasses (48, 2312; 47, 1377b, 2684). Massive spread of inoculum over long distances by air currents has been demonstrated in Europe, India and N. America (45, 1784; 46, 582; 48, 410). The fact that most races cover a wide area demonstrates that widespread dispersal of inoculum takes place. The new race Heiner which caused an epidemic in the Netherlands in 1955 was found to extend from N. Ireland to Germany and S. Sweden in the following years (Zadoks, 1965).