Physics Objectives for Future Studies of the Spin Structure of the Nucleon

Physics perspectives are shown for future experiments in electron or positron scattering on nucleons, towards a deep and comprehensive understanding of the angular momentum structure of the nucleon in the context of Quantum Chromodynamics. Measurements of Generalised Parton Distributions in exclusive reactions and precise determinations of forward Parton Distributions in semi-inclusive deep inelastic scattering are identified as major physics topics. Requirements are discussed for a next generation of high-luminosity fixed-target experiments in the energy range 30-200 GeV.