This review is primarily concerned with the synthesis, structure and fluxional behaviour of cyclic and acyclic chalcogen-nitrogen systems containing phosphorus(V) or phosphorus(III). The cyclic Ph 4 P 2 N 4 S 2 R - and Ph 4 P 2 N 4 S 2 - 2 anions (and their selenium analogues) are versatile ligands for both early and late transition metals. Mono-, di-, tri- and tetradentate bonding modes have been established for the eight-membered P 2 N 4 S 2 ring in these inorganic heterocycles. Ligation occurs through sulphur (or selenium) and/or nitrogen, while the coordinatively saturated phosphorus(V) centres serve as an informative probe of fluxional processes. By contrast, coordination occurs exclusively through phosphorus in both the cyclic and acyclic phosphorus(III) systems.In order to provide a background for the discussion of the coordination chemistry of hybrid P-N/S-N systems, the review begins with a short account of N-bonded complexes of cyclophosphazenes and S 4 N 4 , which is followed by a discussion of metal complexes of the S 4 N 2 - 4 dianion. The concluding section of the review describes metal complexes of some related anionic S-N ligands. In particular, the alkali metal derivatives of the acyclic [RNS(R )NR ] - anions and transition metal complexes of the cyclic radical PhCN 2 S 2 are discussed.