Four-point correlation functions are observables of significant interest in holographic quantum field theories. In this talk I will describe the computation of a family of four-point correlation functions of operators in short multiplets of 4D N=4 super Yang-Mills theory, by studying the quadratic fluctuations around non-trivial supergravity backgrounds. The supergravity backgrounds are supersymmetric smooth geometries in the family derived by Lin, Lunin and Maldacena. For generic parameters, the supergravity backgrounds are dual to heavy CFT states. However I will also discuss the limit in which the dual CFT states become light single-particle states. The resulting all-light four-point correlators are related by superconformal Ward identities to previously known four-point correlators of half-BPS chiral primary operators. By verifying that the Ward identities are satisfied, we confirm the validity of the supergravity method.

I will describe recent studies of bound states of NS5 branes carrying momentum and/or fundamental string charge, in the decoupling limits leading to little string theory and to AdS3/CFT2 duality. This work involves a class of exactly solvable worldsheet models that describe families of BPS and non-BPS black hole microstates. These models have enabled studies of string and D-brane probes of these microstates, yielding insight into their stringy structure in the gravitational bulk description.

The Information Paradox represents a strong consistency challenge for any quantum theory of gravity. The study of black hole internal structure in String Theory offers the potential to resolve this paradox. I will give an overview of recent work on constructing families of smooth horizonless supergravity solutions describing black hole microstates. Where applicable, I will present a holographic description of these solutions. I will also discuss the physics of an observer falling into a black hole.