Markus Müller is Group Leader at IQOQI Vienna. His group studies foundational problems in theoretical physics from an information-theoretic perspective. The main tool and inspiration is quantum information theory, which they apply to a variety of questions: what are the laws of thermodynamics in the regime of very small or strongly correlated systems? Can we understand the abstract formalism of quantum theory as a consequence of simple operational principles, and how is it related to the structure of spacetime? Finally, what can we learn from this for applications in the device-independent framework of quantum information, for experimental tests of QT, and in the broad context of quantum gravity? They address these questions with the rigorous methods of mathematical physics.