  This brief review introduces the method and application of real-space
renormalization group to strongly disordered quantum systems. The focus is on
recent applications of the strong disorder renormalization group to the physics
of disordered-boson systems and the superfluid-insulator transition in one
dimension. The fact that there is also a well understood weak disorder theory
for this problem allows to illustrate what aspects of the physics change at
strong disorder. In particular the strong disorder RG analysis suggests that
the transitions at weak disorder and strong disorder belong to distinct
universality classes, but this question remains under debate and is not fully
resolved to date. Further applications of the strong disorder renormalization
group to higher-dimensional Bose systems and to bosons coupled to dissipation
are also briefly reviewed.
