String Theory and M-Theory String/superstring theory is an immensely rich framework and the most studied and well-established approach to quantum gravity. Its central thesis is that the basic constituents of matter are strings rather than point-like particles. The mathematical consistency of this simple premise has profound consequences — for example that space-time has six hidden dimensions and that in addition to strings it contains higher dimensional objects, known as branes. There are several string theories all of which are avatars of a strongly interacting theory called M-theory, where the strings are replaced by membranes. In its 50-year history, the theory has had a profound influence on varied fields in mathematics and physics, giving rise to mirror symmetry, the AdS/CFT correspondence, higher dimensional field theories and insights on the microstates of black holes. As string theory includes both gauge and gravitational interactions, it provides a natural framework for the unification of all of fundamental physics, which awaits experimental confirmation. As one of the most extensive theories ever constructed, much of the research in the group relies on string theory and/or develops it and its applications further.