A single-valued double many-body expansion potential energy surface is reported for ground-state HN2 by fitting accurate ab initio energies that have been suitably corrected by scaling for the H-N-2 and N-NH regions. The energies of similar to900 geometries have been calculated at the multireference configuration interaction level, using aug-cc-pVQZ basis sets of Dunning and the full valence complete active space wave function as reference. The topographical features of the novel global potential energy surface are examined in detail.