The nucleon-nucleon interaction and the quark models

This talk refers to hadronic systems described in terms of quarks and gluons or flux-tubes. We discuss problems which arise in the derivation of the nucleon-nucleon interaction from one-gluon exchange. Particular attention is paid to the classification scheme of six-quark states. We propose a scheme based on molecular-orbitals and valid both for non-relativistic and relativistic quark models.