Trimethylsulfonium is a quaternary ammonium compound with the chemical formula C₃H₉S⁺. It consists of a sulfur atom bonded to three methyl groups and carries a positive charge. This compound is often found in various biological systems and can play a role in cellular processes. Trimethylsulfonium is commonly associated with dimethylsulfoniopropionate (DMSP), a compound produced by marine algae. DMSP serves as an osmolyte and is involved in the production of dimethyl sulfide (DMS), which contributes to cloud formation and climate regulation.