Dark matter constitutes more than 5/6 of the matter in the universe, but its nature and interactions remain one of the great puzzles of fundamental physics. Dark matter collisions or decays have the potential to produce high-energy particles; such particles could be observable by Earth-based telescopes in the future, and may already have reshaped the history of our universe. I will discuss possible astrophysical and cosmological signatures of new dark matter physics, from the epoch before reionization to the present day. One such possible signal is a puzzling excess of gamma-rays emitted from the center of our galaxy; I will argue that while this excess does have many properties suggestive of dark matter annihilation, it is more likely to be the first sign of an unexpected population of pulsars.