This paper briefly introduces the physics behind photoacoustic (listening to light) and acousto-optic (looking at
sound) phenomena and describes several applications for fundamental or applied material research. The
exploitation of a photoacoustic cell for the thermal characterization and depth profiling of liquid crystals is
illustrated. It is illustrated that a photoacoustic cell can be used to study the magnetocaloric effect, and thus to
investigate thermal and magnetic material properties. It is shown that optically excited and detected acoustic
waves in materials can be very helpful to investigate their microscopic structure. In the impulsive stimulated
scattering technique the mechanisms of converting light into thermal, acoustic, orientational and structural
modes is exploited to simultaneously obtain information about the many physical properties of relaxing liquids.