The high-resolution photoelectron spectrum of KrO- was obtained using slow electron velocity-map imaging (SEVI). The SEVI spectrum reveals numerous vibronic transitions between multiple electronic states of KrO- and KrO, both of which are open-shell species. Detailed assignments are made by comparison with theoretical simulations based on high level ab initio calculations and an atoms-in-molecule model that accounts for spin-orbit coupling in the anion and neutral. Several KrO- and KrO vibrational frequencies and excited-state term energies are accurately determined from the analysis of the experimental spectra and are found to be in good agreement with the calculated values.