I consider methods of indirect detection of dark matter annihilation, including astrophysical foreground modeling, techniques for background removal, and current and predicted limits to the dark matter annihilation and decay rate. Dark matter signals from several sources are considered: the center of the Milky Way Galaxy, the Milky Way Galactic halo, diffuse extragalactic emission, and dwarf galaxies.

The strongest dark matter signal is expected to come from the inner degrees of the Galaxy. With the signal and background regions from the High Energy Spectroscopic System (HESS) collaboration from the Galactic center, I derive the strongest constraints on TeV-scale dark matter. I consider a number of dark matter models, including those with Sommerfeld-enhanced cross-sections, and show that the HESS Galactic center observations are in tension with many of these dark matter models. At lower energies in the Galactic center, the Wilkinson Microwave Anisotropy Probe (WMAP) sees extended emission, the "WMAP haze", which is consistent with the synchrotron radiation from a population of high-energy electrons and positrons. Comparing the electron and positron emission from pulsars and dark matter annihilation in the as a source for this synchrotron emission, the two sources show morphological differences, with dark matter giving a more sharply-peaked flux profile and pulsars giving a more extended profile. Both sources give signals consistent with the WMAP haze, but future experiments should be able to identify the source of the emission based on morphology.

I also discuss the modeling of blazars, one of the largest foregrounds in the extragalactic gamma-ray sky. I present a model of blazars which yields gamma-ray flux consistent with the diffuse gamma-ray background (DGRB) radiation observed by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. Specifically, I model the emission from blazars with a luminosity-dependent luminosity evolution model for the blazar gamma-ray luminosity function and use a blazar spectral energy distribution for the blazar emission spectra. By extending this model to the Fermi-LAT 5-year sensitivity, I show that the DGRB will decrease by a factor of 2-3 with five years of Fermi-LAT observations. An analysis of the DGRB is used to constrain the cross-section of dark matter annihilations for several dark matter annihilation channels and masses, and I include a predicted constraint from the Fermi-LAT 5-year DGRB forecast. I also consider the effects of gamma-rays from inverse-Compton emission on the dark matter annihilation signal and consider the dark matter cross-section limits when including this effect.

I conclude with the expected sensitivity of the water Cherenkov detector to high-mass annihilating dark matter from both the Galactic center and dwarf galaxies. At high dark matter masses, the High Altitude Water Cherenkov (HAWC) Observatory should be more sensitive to dark matter in dwarf galaxies than prior experiments.