AbstractThis chapter discusses the genus Allium spp. in terms of general characteristics; distribution, ecology and domestication; and phylogeny and classification. The other topics covered include: the section Cepa (morphology, distribution and ecology; cytological limitations; grouping of the species; enumeration of the species); Allium cepa (description and variability; infraspecific classification; evolutionary lineages; history of domestication and cultivation); other economic species (garlic and garlic-like forms; taxa of Asiatic origin; chives and locally important onions from other areas).