Photothermal spectroscopy relies on the detection of thermal or acoustic waves generated by the absorption of optical radiation and subsequent radiationless deexcitation. With this technique the absorbed energy is detected directly. Hence, weakly absorbing, opaque and scattering samples can be addressed readily by this spectroscopy. Various detection schemes and the underlying physical principles, as well as a number of typical applications demonstrating the potential of this technique are reviewed. © 1986 Springer-Verlag.