H2 membrane separation technology has been identified as a key enabling technology for hydrogen as future energy carrier, in particular in conjunction with the capture and storage of CO2. Improved Pd-alloys and composite membrane structures are needed for this to become viable. In this chapter, the factors affecting the stability of Pd-based membranes, focusing particularly on the effect of structural changes and gaseous contaminants under long-term operation, are described. Approaches to enhance the stability and tolerance are introduced and discussed. Subsequently, an overview of the main application areas of Pd-based membranes is given, along with the stability demands of these applications. Finally, relevant long-term studies focusing on membrane stability are reviewed. It is concluded that considerable progress has been made with respect to the stability, with some applications close to commercialisation. Certain contaminants remain an issue, however, that are likely to require additional developments in gas cleaning technologies.