Part I deals with the supra-specific classification of the subfamily Cyperoideae (excluding the tribe Rhynchosporeae) on a world-wide basis. It involves a broad survey of comparative exomorphic and endomorphic characters, with an analysis and synthesis of all available information from the literature. Many microscopic features of the leaf, culm, glume; hypogynous perianth bristle, stamen, style, stigma and fruit have been examined, many of them for the first time. Most of these features, together with the already known characters commonly used in the classification of genera in the subfamily Cyperoideae, have been employed to form the basis of the supra-specific classification presented here. The two large Linnaean genera, viz: Scirpus and Cyperus, have been split into a number of small, natural genera. Four distinct taxa, previously included in Scirpus a.l., are for the first time accorded generic status, though formal generic names have not been given to 3 of these. These 3 unnamed genera have been temporarily called Genera A, B and C. Cyperus, in the restricted sense used here, is found still to be partly unnatural, but further studies are needed before attempting to change its circumscription. Of the 47 genera adopted in this work, 25 are monotypic and/or geographically restricted; the rest being widely distributed. The maximum concentration of species and genera is found to occur in the tropics. Formal taxonomic treatments have been given to all the 47 genera in the conclusion, except for those genera which were not personally investigated; for the latter only keys for their identification and appropriate literature references have been given. An informal tribal and subtribal grouping has been proposed to accommodate the narrower, more natural genera adopted, since the limits of the traditional tribes Cypereae and Scirpeae no longer stand. New nomenclatural combinations, as well as the list of species and citation of voucher specimens studied anatomically, have been given in Appendices. Part II deals with the revision of the entire subfamily Cyperoideae as it is represented in the area covered by the Flora of Turkey (Davis 1965-). 47 species representing 21 genera are found in this area. This number includes taxa either seen by me or accepted from reliable records in the literature. Descriptions, synonymy, habitats, specimen citations on a grid basis, notes on the variability of Turkish species, and a key for their identification have been included in this account. Two new taxa have been discovered, for which English diagnoses have been given. Finally, an attempt has been made to explain some of the apparent disjunctions in the distribution of certain species in Turkey.