The production of herbicide resistant plants using molecular and cellular techniques, including mutant selection, cloning, plant transformation and protoplast fusion, is discussed in relation to the mode of action of the herbicide as well as the alternative molecular strategies of modification of target protein, introduction of detoxifying system or overproduction of target protein. Successful attempts to modify the tolerance of plants to the herbicides atrazine, sulphonylureas, bromoxynil, glyphosate and phosphinothricin using cellular and molecular techniques are reviewed.