Conductivity data provide only limited insight into transport mechanisms in polymer electrolytes. Because the cation-polymer and anion-polymer interactions are fundamentally different, it is likely that the motion of cations on an atomic scale takes place by a different mechanism from that of anions. There is evidence that ion pairs may be mobile in some circumstances. It has also become apparent that it is necessary to consider the effect of varying the relative molar mass of the host polymer on the ionic motion. In this paper, we discuss recent electrochemical measurements and results from ion diffusion studies using pulsed field gradient nuclear magnetic resonance, and attempt to analyse these data in terms of possible ion transport mechanisms.