The experimental use of anti-microtubule compounds has revealed essential functions of microtubules in plant cytoskeletal arrays, including the pre-prophase band, the mitotic and meiotic spindles, the phragmoplast, and the cortical array. The most commonly used plant microtubule depolymerization compounds are colchicine, and several synthetic herbicides belonging to three different chemical classes, the dinitroanilines, phosphoric amides, and N-phenyl carbamates. Taxol, a secondary plant product, is the only drug found to promote the polymerization of plant microtubules. This paper summarizes our current understanding of the biochemical interactions of colchicine, anti-microtubule herbicides, and taxol with plant tubulin and microtubules.