This chapter studies the genus Zygoascus. Asexual reproduction is by multilateral budding; pseudohyphae are formed and septate hyphae may also be present. Blastoconidia are formed on pseudohyphae and true hyphae. Hyphal septa have micropores. The species of the genus are homo- or heterothallic. Asci are obovate to spherical and are formed after conjugation between a cell and its bud, between independent cells, or after fusion of hyphal cells. Asci are persistent and contain one to four hemispherical to galeate ascospores. The chapter also discusses physiology/biochemistry and phylogenetic placement of the genus in which sugars are fermented, nitrate assimilation varies among species, and the diazonium blue B reaction is negative, where determined coenzyme Q-9 is the primary ubiquinone. The type species taken is Zygoascus hellenicus. In this chapter the genus Zygoascus is characterized by the production of budding cells, pseudohyphae, septate hyphae, and asci with one to four hemispherical to galeate ascospores, which have a distinct electron-dense base. ?? 2011 Copyright ?? 2011 Elsevier B.V. All rights reserved.