The novel chlorosulfuryl chloroformate, CIC(O)OSO2CI, was prepared by the reaction of CCl4 and SO3. Alternatively, the compound was obtained from the direct insertion reaction of SO3 to Cl2C=O. The latter reaction constitutes also a confirmation of the proposed mechanism for the former one. Density functional theory and MP2 theoretical approximations predict the existence of two conformers, syn gauche and syn anti, depending on the value adopted by the dihedral angles O(CI-C-O-S) and phi(C-O-S-CI). The structure of the syn gauche conformer was determined by gas-phase electron diffraction (GED). The existence of the syn anti conformer can be neither confirmed nor excluded by the GED experiment. Vibrational spectra (vapor-phase and argon-matrix Fourier transform infrared and liquid Fourier transform Raman) were interpreted by an equilibrium mixture between both conformers.