AbstractThe North American genusCeratagalliaKirkaldy, 1907 is redefined to include subgenusAceratagalliaKirkaldy, 1907 (=IoniaBall, 1933, syn.nov.) with 78 species in two subgenera. Two additional new species are unplaced to subgenus:C. aceratafrom Oregon, andC. emarginatafrom Mexico. The typical subgenusCeratagalliahas 30 species, includingC. gillettei(Osborn & Ball, comb.nov.),C. sordida(Oman, comb.nov.), and two new speciesC. anafrom Mexico andC. viperafrom Washington state. SubgenusAceratagalliahas 46 species, all new combinations underCeratagallia. The economic "species" formerly known as "sanguinolenta" is divided into the Canadian clover leafhopperC. humilis(Oman) and the American clover leafhopperC. agricolasp.nov. Other new taxa in subgenusAceratagalliainclude 18 new species and seven new subspecies:alaskana(ssp. ofsiccifolia)from Alaska;omanion the Pacific coast from Oregon to British Columbia;clinoandlophiafrom the Oregon interior;compressa(ssp. ofsiccifolia),gallus,modesta,okanagana, andzacki(ssp. ofnanella) from intermontane valleys of the Pacific northwest and southwestern mountains;interior(ssp. ofhumilis) androssifrom the Sonoran subregion;australis(ssp. ofnanella),coma,ebena,entoma,falcata,oionus, andvenosafrom Mexico and Texas;alvarana(ssp. ofhumilis),cerea,cristula,harrisi, semiarida, andviatorwidespread between the Appalachian and Rocky Mountains; andwhitcombi(ssp. ofrobusta) from Florida to Arizona. Four former species are reduced to subspecies:compactaOman andpoudrisOman inC. robusta(Oman),helveolaOman inC. cinerea(Osborn & Ball), andtruncataOman inC. humilis. The taxa are keyed and illustrated, and their phylogeny is discussed.