We describe a generalizable approach to the development of phase transferable effective intermolecular potentials and apply the method to the study of N-2 The method is based on a polarizable shell model description of the isolated molecule and uses experimental data to establish the parameters. Consideration of the Ne dimer shows this to be a conceptual advance over point polarizability descriptions of atomic interaction. Our parametrization of N-2 accurately describes not only the molecule’s electrostatic field (i.e., a practical representation of the molecular charge distribution) but also its response to electrical and mechanical stress (polarization and deformation). The purely intermolecular terms in our potential reflect shell-shell interactions. These are parametrized by fitting properties of the low temperature solid phase of nitrogen. We derive a phase transferable potential able to account for the second virial coefficient of the gas phase, the pressure induced phase transition between nitrogen’s cubic and tetragonal phrases, and a wide range of liquid properties (pair distribution function, heat of vaporization, self-diffusion coefficient and dielectric constant).