This is an expert and illuminating review of the leading models of nuclear structure: effective field theories based on quantum chromodynamics; ab initio models based on Monte Carlo methods employing effective nucleon-nucleon interactions; diagonalization and the Monto Carlo shell model; non-relativistic and relativistic mean-field theory and its extensions; and symmetry-dictated approaches. Theoretical advances in major areas of nuclear structure are discussed: nuclei far from stability and radioactive ion beams; gamma ray spectroscopy; nuclear astrophysics and electroweak interactions in nuclei; electron scattering; nuclear superconductivity; superheavy elements. The interdisciplinary aspects of the many-body problem are also discussed. Recent experimental data are examined in light of state-of-the-art calculations. Recent advances in several broad areas of theoretical structure are covered, making the book ideal as a supplementary textbook.