Maleic acid (MA) is a dicarboxylic acid that undergoes esterification with ethanol in the presence of cation-exchange resin catalysts to form diethyl maleate. Its crystalline structure has been analyzed. Reaction kinetics and mechanism of the isomerization of maleic acid to fumaric acid in the presence of ceric and bromide ions has been investigated. The reaction mechanism and reactivity ratios for the radical copolymerization of maleic acid with styrene have been determined.