The photodissociation dynamics of gas phase I-3(-) following 390 nm excitation are studied using femtosecond photoelectron spectroscopy. Both I- and I-2(-) photofragments are observed; the I-2(-) exhibits coherent oscillations with a period of 550 fs corresponding to similar to 0.70 eV of vibrational excitation. The oscillations dephase by 4 ps and rephase at 45 and 90.5 ps on the anharmonic I-2(-) potential. The gas phase frequency of ground state I-3(-) is determined from oscillations in the photoelectron spectrum induced by resonance impulsive stimulated Raman scattering. The dynamics of this reaction are modeled using one- and two-dimensional wave packet simulations from which we attribute the formation of I- to three-body dissociation along the symmetric stretching coordinate of the excited anion potential. The photodissociation dynamics of gas phase I-3(-) differ considerably from those observed previously in solution both in terms of the I-2(-) vibrational distribution and the production of I-.