Mankind’s demands for high quality water resources, arable land and fossil fuels are greater than the sustainable supply in many countries. The perennial grass Arundo donax (Adx), giant reed, produces more cellulosic biomass (over 45 dry t/ha/year when irrigated with wastewater) using less land, fertilizer and without pesticides than any alternative crop reported for Mediterranean to sub-tropical environments. Adx is a second generation biofuel crop (a non-food, cellulosic biomass feedstock for bioethanol, or combustion for heat and power and carbon credits). In the first year, Adx planted in a former salt evaporation basin near Barmera, South Australia produced a high biomass yield of 45.2 t/ha of oven dry tops when irrigated with up to 9 dS/m winery wastewater with no pesticide use. In South Carolina, USA, Adx was grown with diluted sludge irrigation and a salt tolerant stand of Adx was monitored on a tidal creek bank, which received over 90% of seawater salinity. Based on these studies, we classed Adx as a halophyte. Nutrient removal was dependent on plant age at harvest and nutrient supply. Adx is invasive in certain riparian systems in many countries, but without rapidly flowing water to distribute stem and rhizome fragments, it is limited in its natural dispersal ability. Microscopic studies indicated no pollen and no embryo development, which resulted in total sterility (no seed). Therefore, a weed risk management strategy needs to focus on restricting vegetative spread, through selection of appropriate planting sites in the landscape (no plantations in riparian zones) and crop hygiene. Future research on yield, bioconversion, genetics, weed risk and salt tolerance is discussed.