Abstract: Heavy fermion systems are a new but difficult research field in condensed matter physics, their low energy scale and novel physical properties being of particular interest. This paper first briefly introduces some of their basic concepts, then describes the application of angle- resolved photoemission spectroscopy (ARPES) to heavy fermion systems, which includes the characterization of the hybridization between f-electrons and conduction electrons, the hybridization and magnetism of f-electrons, the relationships between f-electron hybridization and quantum critical transitions and superconductivity, and the effect of doping on hybridization. Finally, some unsolved problems in the use of ARPES in heavy fermion systems are addressed, and some solutions suggested.