This chapter describes the characteristics, origin and spread of the causative agents of wheat blast, based on the experience of managing this disease in Brazil (where the first wheat blast epidemic was reported, in 1985, which still causes great losses). Although many aspects of the disease’s occurrence and control remain unknown, some advances have been made. It has been proposed that the origin of wheat blast was through the clonal propagation of an epidemic lineage of Pyricularia oryzae, derived from populations of the fungus growing on an unknown species within the family Poaceae. Recently, it was reported that wheat blast is caused two fungal species, Pyricularia oryzae, patothype Triticum, and a new species that has been described as Pyricularia graminis-tritici. Assays conducted under controlled conditions showed that Pyricularia graminis-tritici isolates were more virulent to Brachiaria (Urochloa sp., ex Brachiaria sp.; a pasture species common to Brazil) than many isolates of Pyricularia oryzae, pathotype Triticum. In addition, it has been determined that insensitivity to strobilurin fungicides is completely distributed in the Brazilian population of the causative agents of wheat blast.