  I discuss contributions to the diffuse gamma-ray background from decay and
annihilation of weakly interacting massive particles (WIMPs). I first review
the calculation of the cosmological abundance of a WIMP and show that it is
simply related to the cross section for annihilation of the WIMP into lighter
particles. The diffuse extragalactic background radiation (DEBRA) from WIMP
decay is then discussed. I show how observational upper limits to the DEBRA can
be used to constrain properties of WIMPs that decay to photons, and I present
additional new constraints that unitarity of the annihilation cross section
imposes on such particles. I then discuss gamma rays from annihilation of WIMPs
in the halo, spheroid, and disk of our galaxy, as well as those from WIMP
annihilation in the Large Magellanic Cloud. (To appear in The Gamma Ray Sky
with Compton GRO and SIGMA, proceedings of the School, Les Houches, France,
January 25-February 4, 1994.)
