Hückel molecular orbital (HMO) theory is applied to (1) the bond lengths in phosphazenes arising from inhomogeneous substitution or complex formation, (2) conjugation between exocyclic groups and the ring and its consequences, and (3) chemical reactivity, carbanion stabilization and molecular rearrangements. Such bond characteristics as order, polarizability and electron localizability depend differently on relative orbital electronegativity. Ring size effects distinguish interactions of different symmetry types. Necessary theoretical improvements are briefly considered.