The authors propose and motivate a precise equivalence between uncompactified eleven-dimensional M-theory and the $N = \infty$ limit of the supersymmetric matrix quantum mechanics describing D0 branes. They present evidence for this conjecture, including correspondences between the two theories and the inclusion of membrane states required by M-theory as excitations of the matrix model. The model appears to be a nonperturbative realization of the holographic principle, with the membrane world volume being a noncommutative geometry embedded in a noncommutative spacetime. The conjecture is supported by the ability of the matrix model to describe the properties of massless, well-separated particles in supergravity theory and the emergence of supergravitons and large metastable classical membranes. The authors also discuss the implications of their conjecture for the dynamics of M-theory, including the long-range interactions of supergravitons and the size of supergravitons, and show that the matrix model membranes correspond to M-theory membranes in terms of their tensions.The authors propose and motivate a precise equivalence between uncompactified eleven-dimensional M-theory and the $N = \infty$ limit of the supersymmetric matrix quantum mechanics describing D0 branes. They present evidence for this conjecture, including correspondences between the two theories and the inclusion of membrane states required by M-theory as excitations of the matrix model. The model appears to be a nonperturbative realization of the holographic principle, with the membrane world volume being a noncommutative geometry embedded in a noncommutative spacetime. The conjecture is supported by the ability of the matrix model to describe the properties of massless, well-separated particles in supergravity theory and the emergence of supergravitons and large metastable classical membranes. The authors also discuss the implications of their conjecture for the dynamics of M-theory, including the long-range interactions of supergravitons and the size of supergravitons, and show that the matrix model membranes correspond to M-theory membranes in terms of their tensions.