Used primarily as a methylating agent in organic synthesis, enabling the introduction of methyl groups to various substrates such as phenols, amines, and carboxylic acids. It is particularly useful in the production of pharmaceuticals, agrochemicals, and dyes due to its high reactivity and selectivity under mild conditions. Commonly employed in liquid or solid form for quaternization reactions, it facilitates the synthesis of surfactants and cationic compounds used in fabric softeners and biocides. Its application extends to analytical chemistry for derivatization of compounds prior to chromatographic analysis. Safe handling is essential due to its corrosive and moisture-sensitive nature.