Composite polymeric electrolytes form a new group of solid ionic conductors. Several desirable properties make them suitable for application in various electrochemical devices working over a wide temperature range. In this paper some recent developments in the field of composite polymeric electrolytes are described. A comparison between the properties of composite electrolytes containing inorganic and organic fillers is made. This is based on conductivity data obtained from impedance spectroscopy and structural characteristics based on FT-IR, NMR, DSC and EDX methods. A novel concept concerning the mechanism of ionic transport in composite polymeric systems is proposed.