The maximally supersymmetric supermembrane theory in space-time dimension D = 11 is a model ‘beyond’ string theory that incorporates D = 11 supergravity as a `low energy limit', and is thus a candidate theory for a non-perturbative formulation of superstring theory. In this talk I will review some basic features, in particular the reformulation of this theory as a one-dimensional gauge theory of area preserving diffeomorphisms, which naturally leads to the matrix model of M theory. I will also mention very recent work (arXiv:2109.00346) to argue that this framework allows for a systematic investigation of the small and large tension limits of this theory.