The infrared (3200-40 cm(-1)) spectra of gaseous and solid 1,1-dicyclopropylethene, (C-C3H5)(2)C=CH2, along with the Raman (3200-40 cm(-1)) spectra of liquid and solid phases, have been recorded. The major trans-gauche (C=C bond trans to one ring with the other ring rotated about 60degrees from the C=C bond, trivial C-1 symmetry) and gauche-gauche (the two three-membered rings rotated oppositely about 60degrees from the C=C bond, C-2 symmetry) rotamers have been confidently identified in the fluid phases, but no definitive spectroscopic evidence was found for the gauche-gauche' form (the two three-membered rings rotated to the same side about 60degrees from the C=C bond, C, symmetry), which is calculated to be present in no more than 6% at ambient temperature. Variable-temperature (-55 to -100 degreesC) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. Utilizing six different combinations of pairs of bands from the C-1 and C-2 conformers, the average enthalpy difference between these two has been determined to be 146 +/- 30 cm(-1) (1.75 +/- 0.36 kJ(.)mol(-1)), with the C-1 form more stable. Given statistical weights of 2:1:1 respectively for the C-1, C-2, and C-s forms, it is estimated that there are 75 +/- 2% C-1 and 19 +/- 1% C-2 conformers present at ambient temperature. By utilizing predicted frequencies, infrared intensities, Raman activities, and band envelopes from scaled MP2(full)/6-31G(d) ab initio calculations, a complete vibrational assignment is made for the C, form and a number of fundamentals of the C2 conformer have been identified. The structural parameters, dipole moments, and conformational stabilities have been obtained from ab initio calculations at the level of Hartree-Fock (RHF), the perturbation method to second order with full electron correlation (MP2(full)), and hybrid density functional theory (DFT) by the B3LYP method with a variety of basis sets. The predicted conformational stabilities from the MP2 calculations with relatively large basis sets are consistent with the experimental results. Structural parameters are estimated from the MP2(full)/6-311+G(d,p) predictions which are compared to the previously reported electron diffraction parameters. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.