A systematic study of all possible tetraatomic P2N2 structures has been made at the B3LYP/6-311+G(2df) and CASPT2(12e,12o)/ANO-L levels. A closed-shell butterfly C 2 v structure (A) is predicted to have the lowest energy on the tetraatomic P2N2 potential energy surface. The energies for dissociation of P2N2 to two P⋮N or to N2 and P2 have been examined. A closed-shell quasi-tetrahedral C 2 v structure of P2N2 (B) and a linear open-shell singlet P−N⋮N−P (E*) have been found to be kinetically stable to fragmentation or rearrangement at the CASPT2/ANO-L level. Several transition states have significant biradical character which reflects the orbital crossings that are found along reaction paths of least motion. The fragmentation reaction of P−N⋮N−P to 2P⋮N involves a trans-bent transition state that has a strong similarity to a known transition metal reaction.