Elymus sect. Caespitosae and sect. Elytrigia in Iran are revised, a key to the taxa, synonymies, descriptions, quotation of selected collections, data on geographical distribution, and additional notes, where necessary, are presented. The genus is treated in a broad sense, as comprising the genera Elytrigia, Pseudoroegneria, Thinopyrum, Lophopyrum, and Trichopyrum. The combinations Elymus pertenuis, E. tauri var. kosaninii, E. elongatiformis, E. hispidus var. podperae and E. hispidus var. villosus are formed as names new to science. Elymus nodosus subsp. dorudicus and E. gentryi var. ciliatiglumis are described as subspecies and variety new to science, respectively.