Mesaconic acid, also known as trans-2-methyl-2-butenedioic acid, is an unsaturated dicarboxylic acid. It is a structural isomer of citraconic acid and fumaric acid. The compound is a white crystalline solid at room temperature. Its primary role is as a versatile organic synthetic building block. The conjugated double bond and two carboxylic acid groups make it a useful precursor for the synthesis of various polymers, resins, and specialty chemicals. It can undergo addition reactions, esterification, and polymerization. It is also investigated as a potential monomer for biodegradable polymers. While not a commodity chemical, mesaconic acid finds niche applications in research and development for creating functional materials. It is also a metabolite found in some biological pathways.