Ab initio local-density functional total-energy calculations indicate that a polymeric form should be the stable phase of nitrogen above [approximately] 35 GPa, and that such a polyermic phase is likely to be both energetic and metastable at atmospheric pressure. These results also suggest that such a polymeric form of nitrogen may survive metastably at atompsheric pressure as an energetic, high-melting temperature, insulating solid, with a specific enthalpy of 6.7--14.1 MJ/kg. While this does not exceed the Air Force HEDM goal of 15 MJ/kg, such a material may nevertheless compare favorably with existing monopropellants. 2 figs., 24 refs.