Dense composite Pd and Pd/alloy membranes are currently being extensively investigated. The synthesis and characterization of these membranes, with a special emphasis on Pd/alloy membranes, are reviewed in this paper. Experimental results on Pd/Cu membranes supported on porous stainless steel exhibited good thermal stability and reasonable hydrogen flux. Furthermore, optical micrographs showed the formation of the dense palladium layer was unaffected by the topological features of the porous stainless steel, although the surface of the support directs the topology of the final Pd layer.