Abstract
In the light of the description of the nucleon-nucleon potential in terms of meson-exchange, the author discusses the most interesting contributions to the nuclear wave function, paying particular attention to 2 pi exchange associated with isobar components in the wave function. Direct evidence for mesonic degrees of freedom in nuclei is revealed by electromagnetic interactions, giving rise to the so-called meson exchange currents. They detail the important aspects of these currents at low and medium energies by studying neutron radiative capture by protons and deuterons on the one hand, and the photodisintegration of the deuteron on the other hand.