A sketch of the various formulations of the theoretical optical potential for scattering processes.- Equivalent potentials in the description of scattering processes.- Green function approach to single particle states in nuclei.- Many-body theory of the optical-model potential.- Optical model potential and nuclear density distributions.- Non-local optical potential: Theoretical and phenomenological aspects.- The systematics of the 1f7/2 neutron single-particle energies.- Small angle elastic scattering of polarized protons.- Dispersion relation analyses of the energy dependence of the optical potential.- Theoretical investigations of the optical-model potential.