Photodetachment of the acetate anion, CH3CO2-, and the subsequent dissociation dynamics of the CH3CO2. radical were studied using photoelectron-photofragment coincidence spectroscopy at 355 and 257 nm. An upper limit to the adiabatic electron affinity (EA) of CH3CO2., EA = 3.47 +/- 0.01 eV was determined. Evidence for several low-lying electronic states of the CH3CO2. radical were observed in the photoelectron spectra. Most CH3CO2. radicals dissociated to CH3. + CO2 products with a large kinetic energy release ( /E-avi = 0.72 for 355-nm excitation) and an anisotropic angular distribution (beta similar to 1.2), while -10% of CH3CO2. radicals were stable on the microsecond time scale at both wavelengths. Structured near-threshold photoelectron spectra at 355 nm were similar when photoelectrons were recorded in coincidence with either stable radicals or dissociation products, indicating a sequential dissociative photodetachment. Experiments were also carried out on CD3CO2- to aid in the interpretation of the photoelectron spectra and deduction of the dissociation mechanism.