The Pooideae is one of the largest subfamilies of grasses with approximately 150 genera and 3,300 species. To address unresolved questions concerning phylogeny and systematics of the subfamily Pooideae, molecular phylogenetic analyses were carried out using the chloroplast gene region matK–3’trnK and the nuclear internal transcribed spacers (ITS). Furthermore, morphological characters were extensively examined and discussed with respect to molecular, cytogenetic and biogeographical data. The new findings give strong evidence to modify the taxonomic treatment of major lineages within this subfamily. The following classification of Pooideae is proposed: Brachyelytreae, Nardeae with the subtribes Nardinae and Lygeinae, Meliceae with the subtribes Brylkiniinae and Melicinae, Duthieeae, Phaenospermateae, Stipeae with the subtribes Ampelodesminae and Stipinae, Diarrheneae, Brachypodieae, Hordeeae (syn. Triticeae) with the subtribes Brominae, Hordeinae and Littledaleinae and the Aveneae/Poeae tribe complex. Furthermore, the study shows that the small grass tribe Hainardieae is highly polyphyletic. Its genera are members of different groups among the Aveneae/Poeae tribe complex. In conclusion, the thesis gives new insights into the classification of the grass subfamily Pooideae, including the description of the new tribe Duthieeae and a revised treatment of the tribes Nardeae and Hordeeae.