We report a high-resolution photoelectron imaging and photodetachment spectroscopy study of cryogenically cooled IO-. The high-resolution photoelectron spectra yield a more accurate electron affinity (EA) of 2.3805(5) eV for IO as well as a more accurate spin-orbit splitting energy between the (2)Pi(3/2) and (2)Pi(1/2) states of IO as 2093(5) cm(-1). Photodetachment spectroscopy confirmed several excited states for the IO- anion predicted by theoretical calculations, including two valence-type excited states, the repulsive (3)Pi state, and a shallow bound (1)Pi state. More interestingly, we have observed two vibrational resonances which are proposed to be due to a dipole-induced resonant state, about 230 cm(-1) above the detachment threshold of IO-.