Non-nucleonic degrees of freedom in the nucleus must be understood in the nucleonic framework of nucleus in relation with the structure of the nucleons from which mesons are emitted to link the nucleons, and with isobars, mesonic exchange currents, and underlying conservation laws. This topical volume sheds light on these highly exciting non-nucleonic effects extracted as the result of interplay among the constituents including quarks, and on the limit of applicability of various conservation laws.