Disordered systems can be sometimes accurately treated by real-space strong disorder RG, both for the ground and excited states. The general strategy is a sequential elimination of "fast" degrees of freedom. The method becomes asymptotically exact if disorder becomes stronger with renormalization, flowing towards infinite randomness. 

RG can be applied to specific microscopic models [[pekker]], or to effective models of MBL [[vosk]], attempting to capture the MBL-Thermalization transition.