Vertex operators for the supermembrane and background field matrix theory

We derive the vertex operators that are expected to govern the emission of the massless d = 11 supermultiplet from the supermembrane in the light cone gauge. Our results immediately imply the linear coupling of matrix theory to an arbitrary supergravity background to all orders in anticommuting coor dinates. Finally we address the definition of n-point tree level and one-lo op scattering amplitudes. The resulting 3-point tree level amplitudes turn out to agree with d = 11 supergravity and are completely fixed by supersymm etry and the existence of a normalizable ground state.