The valence photoelectron spectra (PES) of gas-phase aminobenzoic acids (meta-, ortho- and para-isomers) were measured using synchrotron radiation and calculated from first principles using Density Functional Theory (DFT) with popular hybrid exchange-correlation functionals and many-body perturbation theory using the perturbative one-shot (G0W0) and eigenvalue self-consistent (GnW0) approaches within the GW approximation. The vibrational structures and line shapes found in the PES were modeled using Time-Dependent DFT. Theory can reproduce the experimental results very well. The photoelectron-photoion coincidence spectra of the ortho- and para-isomers were also measured. They reveal interesting differences in the fragmentation patterns and the influence of metastable states at the onset of fragmentation.