Anion photoelectron spectroscopy (PES) is a versatile experimental technique that enables detailed characterization of the neutral species created when an electron is photodetached from a negative ion. In its canonical manifestation, mass-selected anions are photodetached at a fixed photon energy. The resulting photoelectron kinetic energy and angular distributions reveal information on the energetics, structure, and vibronic spectroscopy of the neutral. Anion PES has provided electron affinities for a wide range of atomic and molecular species. Depending on the photon energy, PES can characterize the ground and electronically excited states of a neutral in a single experimental measurement, yielding term energies and, in favorable cases, vibrational structure in each of the accessible electronic states.