Membrane technologies are being increasingly applied to the processes followed for separating hydrogen and its isotopes. In the fusion fuel cycle, the most important applications of the membranes for tritium purification and recovery are as follows: plasma exhaust treatment, tritium extraction from the breeding blanket and water detritiation. In this chapter, several kinds of membranes that are currently used for separating tritium are being described, with particular focus on the dense Pd-based membranes, which exhibit infinite selectivity to the hydrogen isotopes. In particular, the hydrogen/metal interaction, the hydrogen mass transfer mechanisms through metals and the related isotopic effects are being reported. Beside permeation, other chemical and physical properties of the commercial Pd-Ag alloy used for manufacturing the membrane permeators are being discussed with special regard to the membrane synthesis and the reactor module design. Finally, the process applications of the membrane devices used for the detritiation treatments in the fusion fuel cycle are also being presented. ©2013 Nova Science Publishers, Inc. All rights reserved.