Book excerpt: An introduction to herbicide action; Reaching the target; Oxigen toxicity and herbicidal action; Microtubule disruptors; Herbicide effects on lipid synthesis; Nucleic acid and protein synthesis inhibitors; Inhibition of amino acid biosysnthesis; Herbicides with auxin activity; Other sites of herbicide action; Secondary physiological effects of herbicides; Herbicide interactions with herbicides, synergists, and safeners; Naturally occurring chemicals as herbicides.