In this overview of the topic, catalysis with metal membrane reactors is reviewed along with an assessment of what still needs to be done. This is still an emerging technology with a need for a lot of fundamental research. Palladium and palladium alloy membrane reactors are compared and discussed with regard to technology limitations and needs. Because of the limitations of palladium metal compositions, there is an emerging effort in less costly but high hydrogen permeable metal membranes such as those composed of tantalum or niobium. Finally an extended discussion is provided with regard to what are the critical issues remaining for the successful commercial application of this technology.