Light front meson exchange models for the two-nucleon system which involve interacting spin operators will be analyzed. The Lee model will be extended to provide a Poincare' invariant model for the pion-nucleon system and used to assess the validity of the constituent quark model. A light front reformulation of a covariant harmonic oscillator will be extended to systems of spin-1/2 particles and used to study the relationships between various relativistic and non- relativistic hadron quark models. Electromagnetic currents described by covariant constraint dynamics will be used to calculate form factors and structure functions for two and three quark systems.
