The potential curves and dissociation energies for the ground states of ClO((2)Pi) and ClO-((1)Sigma(+)) and possible low lying excited states ((1)Pi, (3)Pi, (3)Sigma(-), (3)Sigma(+), (1)Delta, etc.) of ClO- have been investigated using sophisticated ab initio quantum mechanical techniques with large basis sets including diffuse functions. The equilibrium bond distance and vibrational frequency for the ground state ((1)Sigma(+)) of ClO- are predicted to be 1.688 Angstrom and 660 cm(-1) at the coupled-cluster single double (triple) [CCSD(T)]/aug-cc-pVQZ level of theory. The lowest excited singlet state of ClO- is predicted to be the open-shell (1)Pi state, which is 2.43 eV higher in energy than the ground state, while the lowest triplet state ((3)Pi) of ClO- has a potential with well depth of 0.32 eV. The adiabatic electron detachment energy from ClO- is predicted to be 2.29 eV including zero-point vibrational energy (ZPVE) at the CCSD(T)/aug-cc-pVQZ level of theory. The spin allowed vertical electronic transition ((1)Sigma(+)-(1)Pi) of ClO- is predicted to be 3.13 eV including ZPVE. The dissociation energies (D-0) of ClO- to Cl-(S-1)+O(P-3), Cl-(S-1)+O(D-1), and Cl(P-2)+O-(P-2) are predicted to be 1.40, 3.46, and 3.61 eV, respectively, including ZPVE.