The ionization energy (IE), electron affinity (EA), and heats of formation (Delta H-f0 degrees/Delta H-f298) for cyclopentadienyl radical, cation, and anion, C5H5/C5H5+/C5H5-, have been calculated by wave function-based ab initio CCSDT/CBS approach, which involves approximation to complete basis set (CBS) limit at coupled-cluster level with up to full triple excitations (CCSDT). The zero-point vibrational energy correction, core-valence electronic correction, scalar relativistic effect, and higher-order corrections beyond the CCSD(T) wave function are included in these calculations. The allylic [C5H5((2)A(2))] and dienylic [C5H5(B-2(1))] forms of cyclopentadienyl radical are considered: the ground state structure exists in the dienyl form and it is about 30 meV more stable than the allylic structure. Both structures are lying closely and are interconvertible along the normal mode of b(2) in-plane vibration. The CCSDT/CBS predictions (in eV) for IE[C5H5+((3)A(1)')<- C5H5(B-2(1))] = 8.443, IE[C5H5+((1)A(1))<- C5H5(B-2(1))] = 8.634 and EA[C5H5-((1)A(1)')<- C5H5(B-2(1))] = 1.785 are consistent with the respective experimental values of 8.4268 +/- 0.0005, 8.6170 +/- 0.0005, and 1.808 +/- 0.006, obtained from photoelectron spectroscopic measurements. The