Tetramethylammonium fluoride tetrahydrate (TMAF) is a quaternary ammonium salt. It serves as a weak base and a fluoride ion source in various organic reactions, such as nucleophilic substitutions, deprotection of functional groups, and ring-opening polymerizations. Unlike other sources of fluoride, TMAF is compatible with numerous functional groups, making it a versatile reagent in synthetic chemistry. Additionally, TMAF is utilized as a fluorinating agent in medicinal chemistry for the preparation of radioactive tracers and in biochemistry for protein modification. The tetrahydrate form of TMAF is more stable and easier to handle than its anhydrous counterpart.