The Raman spectra of the potassium salts of [M(CN)6]3–(M = Co, Fe, Mn, and Cr) and [M(CN)6]4–(M = Fe and Ru), have been measured in the solid state and in aqueous solution and also of solid K4[Mn(CN)]6, 3H2O and K5[Mn(CN)6],H2O. The i.r. spectra of solid K5[Mn(CN)6],H2O, K4[V(CN)6],3H2O, and ‘K3[V(CN)6],H2O’ are also reported. Assignments of fundamental vibrational modes are proposed for the anions on the basis of these measurements and of published i.r. data, and the results are correlated with σ- and π-effects in the metal–cyanide bond.