The use of high-field n.m.r. spectroscopy to study the aqueous chemistry of vanadium(V) has yielded information not only about the species present but, also, a qualitative understanding of the ¹⁷O n.m.r. chemical shifts in polyanions. The peroxo and sulphido complexes of vanadium(V) are reported as well as the interaction of vanadate with ADP and ATP, and oxygen exchange in the polyanion tetradecavanadophosphate (9-) ([PV14O42]9ˉ). In general, peroxovanadate complexes tend to contain two peroxide ligands per vanadium, although some mono-, tri- and tetraperoxovanadates are found. The mono- and diperoxovanadates undergo a change in co-ordination from octahedral to tetrahedral on removal of their final proton ( ̃pH 14). Four new dimeric species have been observed, three of which are unsymmetrical. The pH-dependent differential rates of oxygen exchange of tetradecavanadophosphate (9-) can be explained in terms of the stabilisation of the anion by the two pentaco-ordinate VO caps with respect to the "equator" of the Keggin type structure. The four half-hemisphere units resist exchange. Bulk distortions of this anion and decavanadate (6-) can be deduced from the observation of their 17O chemical shifts with pH. The three known sulphido and oxosulphido- vanadium(V) species [VS4]ɜˉ, [VOS3]ɜˉ and [VO2S2]ɜˉ have been identified by high-field vanadium-51 n.m.r., together with the previously unobserved ions VO3S]ɜˉ, [V2S7]4ˉ, [O3VSVO3]4ˉ, [SO2VSVO2S]4ˉ and the protonated monomers. No equilibria between monomeric species are observed other than for protonation. Vanadate complexes with the polyphosphate chain in both ATP and ADP, probably as [VO2]+ bridging two adjacent phosphates. Exchange with species containing [VO3]ˉ bound to the terminal phosphate and, in ATP only, "[VO]ɜ+ bound to all the phosphates may occur.