[en] Dual models are presented in a second quantized field theory. The field is a functional of a one dimensional path. Its Fock space operators create or destroy an entire string. A free action is constructed using as an additional requirement parametrization invariance. One solution is found to the system, and it corresponds to the free string on null planes. An extensive algebra of constraints is encountered. A global U(1) invariance of the free action is extended to a functionally local one. This introduces minimal couplings to external fields. Self-couplings are introduced in the action to be consistent with local couplings and invariant under this extended symmetry. The self-coupling leads to a perturbation theory whose particle interpretation is the string splitting vertex of Nambu and Mandelstam. Supersymmetry, generalized vector dominance, and the development of a vacuum expectation value are investigated in this language of the dual resonance models. The internal zero point energies cancel in the fermionic model. The paths may be coupled to photons directly as in vector dominance