  A diverse experimental program for the study of the photoproduction of mesons
off nuclei has been carried out - and is still running - at the Mainz MAMI and
Bonn ELSA electron accelerators with the TAPS, Crystal Barrel, and Crystal Ball
calorimeters. It is motivated as a detailed study of the in-medium properties
of hadrons and the meson - nucleus interactions. Typical examples for the
in-medium behavior of vector mesons ($\omega$), scalar mesons ($\sigma$), and
nucleon resonances (P$_{33}$(1232), S$_{11}$(1535), D$_{15}$(1520)) are
discussed. Special attention is paid to meson - nucleus final state
interactions.
