This work continues the nuclear theory program of Carl Shakin and Louis Celenza at CUNY Brooklyn. A broad range of problems will be addressed concerning nuclear structure and reactions at mean-field and relativistic energy scales and problems related to the underlying quark substructure of nuclei. The emphasis is on relativistic theoretical frameworks. Some selected topics are the description of nuclear matter using light front dynamics, the general theory of electromagnetic response functions, a comparison of instant and light-front dynamics and light-front structure functions of nucleons.