In-situ IR spectroelectrochemistry was used to investigate the behavior of cyanide (CN-) at polycrystalline platinum surfaces in aqueous perchlorate (ClO4-) electrolyte, IR spectroelectrochemical data reveal the existence of a number of surface, as well as solution, cyanide species in the interfacial region. Within the double-layer potential region, there is IR evidence for several forms of adsorbed cyanide CN(ads)- (nu(max) almost-equal-to 2070 cm-1, nu(max)"’ almoat-equal-to 2145 cm-1, and nu(max) almost-equal-to 2170 cm-1). When the potential is made sufficiently positive, cyanide is oxidized to form cyanate (OCN-) (nu(max) = 2171 cm 1). Other solution cyanide species which may be formed at the platinum/cyanide solution interface include hydrogen cyanide (HCN) (nu(max) = 2095 cm-1) and the square-planar platinum cyanide complex Pt[CN]42- (nu(max) = 2133 cm-1) (IR-active E(u) mode). The interfacial electrochemistry of the PtCN- + ClO4-system was found not only to be influenced by the applied electrode potential, but also to be driven by changes in the interfacial pH, which is potential-dependent. In-situ IR spectroelectrochemistry reveals details of the potential-dependent surface chemistry of the PtCN- system, the complexities of which cannot easily be studied by other techniques.