NOVELTY - A composite membrane comprises a conductive polymer and a support material for the polymer. The polymer contains a moiety, functionalized to provide ion exchange sites.    USE - For a fuel cell or an electrolyzer (claimed); as ion-exchange membranes for electrochemical fuel cells; as proton exchange membrane for water electrolysis; membranes in chloralkali electrolysis; as ion-selection electrodes; as the sensor material for humidity sensors; as ion-exchange material for separations by ion-exchange chromatography; as ion-exchange membranes employed in analytical pre concentration techniques; as ion-exchange membranes in electrodialysis; as membranes in gas separation and pervaporation techniques; and as a bipolar membranes employed in water splitting and subsequently in the recovery of acids and bases from waste water solutions.    ADVANTAGE - The composite membrane is stable when used as polymer electrolyte membrane in the fuel cell. The membrane has high resistance to oxidation, reduction and hydrolysis and has very low permeability to reactants in the fuel cell. The membrane has a high proton conductivity, has high mechanical strength and is capable of being bonded to other components which make up a membrane electrode assembly.    DETAILED DESCRIPTION - A composite membrane comprises a conductive polymer and a support material for the polymer. The polymer contains a moiety of formula (I), (II) and/or (III). At least some of the units (I), (II) and/or (III) are functionalized to provide ion exchange sites. The phenyl moieties in (I), (II) and/or (III) are optionally substituted and crosslinked. -(E-(Ar)-(T3) m-E')- (I) -(T3-CO-(T3) w-G((T3) r-CO-T3) s)- (II) -(T3-SO 2-(T3) 2-G-((T3) t-SO 2-T3) v)- (III)    m, r, s, t, v, w, z=0 or a positive integer;    E and E'=O, S or a direct bond;    G=O, S, a direct bond or -O-Ph-O- moiety;    Ar=T1C(O), T1-C(O)T1, T1C(O)T2C(O)T1, T1C(O)T1, T1SO 2T1, T1-O-T1-O-T1, T1, 9,10-anthracenyl, T1C(Ph) 2T1, 9-bis(T1)-fluorenyl or a group of formula (VIII), (IX), (X);    T1=1,4-phenylene;    T2=1,3-phenylene;    T3=a group of formula (XI).    INDEPENDENT CLAIMS are also included for the following: (1) the conductive polymer and the support material for the polymer comprising polyaryletherketone and/or polyarylethersulfone units; and units of formula -O-Ar' n-O-.    Ar'=sulfonated phenyl groups;    n=integer greater than or equal to 2.    ; and (2) formation of the composite membrane comprising the association of conducting polymer with the support material.