This study is the first specific treatment in Australia of the grasses of a natural region. It gives a taxonomic and ecological account of all known grass species in the arid part of the Northern Territory, an area of about 240,000 square miles. There is a description in technical and general terms of each of the 132 species, with taxonomic keys to genera and species, and with additional data on geographic and land- type distribution, ecological relationships, and economic value. Photographs, with enlargements of spikelet and floret, illustrate 123 of the species.