The ab initio No-Core Shell Model (NCSM) adopts an intrinsic Hamiltonian for all nucleons in the nucleus. Realistic two-nucleon and tri-nucleon interactions are incorporated. From this Hamiltonian, an Hermitian effective Hamiltonian is derived for a finite basis space conserving all the symmetries of the initial Hamiltonian. The resulting finite sparse matrix problem is solved by diagonalization on parallel computers. Applications range from light nuclei to multiquark systems and, recently, to similar problems in quantum field theory. We present this approach with a sample of recent results.