  String theory on AdS3 backgrounds arises as an IR limit of Little String
Theory on NS5-branes. A wide variety of holographic RG flows from the fivebrane
theory in the UV to (orbifolds of) AdS3 in the IR is amenable to exact
treatment in worldsheet string theory as a class of null-gauged WZW models. The
condensate of stringy winding operators which resolves the near-source
structure of fivebranes on the Coulomb branch plays a crucial role in AdS3,
revealing stringy structure invisible to the supergravity approximation. The
D-brane sector contains precursors of the long strings which dominate black
hole entropy in the dual spacetime CFT.
