A review of biological information is provided for Sorghum halepense (L.) Pers., Johnson grass. A native of southern Eurasia to India, S. halepense occurs as a weed in most tropical and temperate areas of the world, and has recently become established in 10 counties in Southern Ontario. Listed as one of the world’s worst weeds, S. halepense infestations result in severe crop losses either from competition or alleleopathic effects and/or by serving as an alternative host for several crop pests. The species is, however, an important forage crop in the southeastern United States and other areas of the world. Johnson grass has several features which contribute to its success as a weed, including the production of extensively creeping rhizomes and large numbers of seeds, rhizomes which regenerate easily if cut into small pieces in cultivation procedures, self-compatibility, seed longevity, seed dormancy and vigorous growth under a wide range of environmental conditions. To date, one population of S. halepense from Brant County, Ontario is known to produce rhizomes which successfully overwinter in Canada. This population would appear to be distinct from the other Ontario populations and is characterized by smaller seeds and seedlings and lower rates of germination. A combination of repeated tillage, proper herbicides and crop rotation will give the best control of Johnson grass.Key words: Sorghum halepense, Johnson grass, biological review