The broad goal of this program is to advance our understanding of quantum gravity starting from nothing more than basic physical principles, such as unitarity, symmetry and causality, by harnessing the AdS/CFT Correspondence and the bootstrap approach of large N conformal field theories. With attention to the question of possible uniqueness of string theory among putative theories of quantum gravity, it is in this holographic sense that we will explore the ''Speakable and Unspeakable in Quantum Gravity'': what features of quantum gravity can be rigorously defined by way of AdS/CFT, and leveraged to classify the space of theories that actually exist? This program will place extra emphasis on low-dimensional holography, which sharpens both the physical puzzles and the mathematical tools used to solve them.