The vapor-phase far-infrared and Raman spectra of 2,3-dihydrothiophene have been recorded and analyzed. The infrared spectra show more than fifty transition frequencies corresponding to Delta v(P) = 1, 2, 3, 4, and 5 transitions. The ring-puckering energy levels were determined for both the ring-twisting ground and excited states. Both one- and two-dimensional potential energy functions, which fit the observed data very well, were determined. The barrier to planarity was determined to be 430 cm(-1) from the one-dimensional model and 435 cm(-1) for the two-dimensional model. The experimental dihedral angle of puckering is 31 degrees, while an ab initio calculation predicts 290. The magnitude of the interaction constant between the puckering and twisting was found to be 1.67 x 10(5) cm(-1)/Angstrom(4), similar to the values determined for related molecules.