What is the effective nuclear Hamiltonian?

Effective Hamiltonians used for nuclear structure calculations are reviewed. The application of fundamental interactions derived from the nucleon-nucleon scattering data to few-body systems and nuclear matter is reviewed. The special problems in defining the effective Hamiltonian for the nuclear shell-model truncation are discussed. Applications of the Skyrme Hartree-Fock (HF) method are presented, and a method for combining HF and shell-model configuration mixing calculations is discussed. (author)