The ionic conductivity of CdI2 doped silver ultraphosphate, metaphosphate and polyphosphate glasses has been reported in this paper. We have observed that the conductivity of metaphosphate and polyphosphate glasses increases and that of the ultraphosphate glasses decreases with the increase of CdI2 content in the compositions. We have observed that insertion of CdI2 expands the host glass network of all compositions leading to increased migration pathway for Ag+ ions. However, the expansion of the glass network is not enough to influence the dynamics of Ag+ ions in ultraphosphate glasses. We have explained the composition dependence of the conductivity of these glasses on the basis of coordination exchange between mobile Ag+ and immobile Cd2+ ions. Due to this exchange effect, Cd2+ and Ag+ ions coordinate to the oxygen and iodine ions respectively. The magnitude of the exchange is different for different phosphate networks and the conductivity can either increase or decrease depending on the magnitude of the exchange. The activation energy for the Ag+ migration depends on the degree of Cd-Ag exchange as well as on the network structure of the glass compositions. (C) 2011 Elsevier B.V. All rights reserved.