Modular Moonshine III. 11 October 1994, corrected 18 Nov 1997 Duke Math. J. 93 (1998), no. 1, 129-154. Richard E. Borcherds, D.P.M.M.S., 16 Mill Lane, Cambridge, CB2 2SB, England. Mathematics department, University of California at Berkeley, CA 94720-3840, U. S. A. www.dpmms.cam.ac.uk/~reb In this paper we complete the proof of Ryba's modular moonshine conjectures [R] that was started in [B-R]. We do this by applying Hodge theory to the cohomology of the monster Lie algebra over the ring of p-adic integers in order to calculate the Tate cohomology groups of elements of the monster acting on the monster vertex algebra.