The tungsten-182 Mössbauer spectra of a series of Keggin structure heteropolytungstates, [EW12O40]n- are reported. There is a very considerable variation in quadrupole coupling at the tungsten nucleus indicating considerable asymmetry in the electron distribution for the more electronegative elements E. The quadrupole coupling correlates well with the structural data, in particular with the distance between the tungsten and the oxygen atom of the EO4 group. These compounds may be regarded as rigid W12O36 cages interacting more or less strongly with an EO4n- host. The spectra of salts of metatungstate [H2W12O40]6- and [W6O19]2- are also given.