The geometric structure and conformational properties of trifluoromethyl chlorosulfonate (chlorosulfuric acid trifluoromethyl ester), CF3OSO2Cl, have been determined by X-ray crystallography, gas electron diffraction (GED), and vibrational spectroscopy (IR(gas), IR(matrix), and Raman(liquid)). These experimental investigations were supplemented by quantum chemical calculations (B3LYP with 6-311G* and 6-311+G(3df) basis sets). All experimental methods result in a single conformer with gauche orientation of the CF3 group relative to the S-Cl bond. The dihedral angle delta(COSCI) is determined to be 91.7(3)degrees in the crystal and 94(3)degrees in the gas phase. This dihedral angle corresponds to a near-eclipsed orientation of the O-C bond relative to one of the S=O double bonds (delta(CO-SO) = -23.0(3)degrees and -21(3)degrees in the crystal and gas phase, respectively).