The various experimental techniques of band-offset determinations in semiconductor heterojunctions are discussed. Special reference is made to their application to (Ga, Al)As/GaAs. We then review heuristic procedures for the band-offset prediction: i) band-edge alignment according to energy-level position of transition metal deep impurities and ii) using differences in Schottky-barrier heights. Finally, we comment on a possible threefold connection between band-edge offsets, deep impurities and Schottky barriers.