Recent progress on proton-conducting Sulfonated Aromatic Polymers is reviewed, including composite and cross-linked ionomers. Proton conductivity and water uptake, studied as function of relative humidity, can be combined to calculate the effective proton mobility in ionomers. The plot of proton mobility versus proton concentration shows common features for various ionomers, which can be related to percolation and tortuosity of hydrated nanometric channels. Proton conductivity can even be enhanced in cross-linked ionomers, possibly due to a reduction of channel tortuosity. (C) 2012 Elsevier B.V. All rights reserved.