AbstractIn this chapter, the taxonomical complexities of the genusTriticumare presented. Following the biological concept of species, the genus contains six species, two diploids, two tetraploid, and two hexaploids. The characteristic morphology of the genus and that of the wild forms, their geographic distribution, and ecological affinities, as well as their preadaptation for domestication and the processes leading to wheat domestication are reported. The origin and evolution of the diploid species, and the genome analysis of the allopolyploids are reviewed. Origin of the A, B, and D subgenomes of allopolyploid wheats, are presented. The relationships betweenTriticumspecies and other Triticineae are discussed.