Our knowledge of the properties of mesons and their interactions with nuclei has come from two sources. Studies of cosmic ray phenomena provided the earliest information. The discovery that mesons may be produced artificially by bombardment of nuclei with radiations from high energy accelerators has, on the other hand, made it feasible to undertake a wide variety of investigations under more controlled conditions than is possible in cosmic ray experiments. In such experiments mesons have been produced by high-energy protons, alpha-particles and neutrons.