A single gamma ray carries millions of times the energy of a single photon of visible light. This means that gamma rays are produced only in the most convulsive environments in the universe – pulsars spinning inside huge magnetic fields, stars in binary systems devouring their partners, and black holes at the centers of galaxies swallowing gas clouds more massive than our sun. The Fermi Gamma-ray Space Telescope was launched on June 11, 2008, to measure these extreme astronomical events. In this lecture, SLAC scientist Eric Charles will describe how we observe astronomical gamma rays and why we must go to space to see them. Then he will discuss how 10 years of observations from the Fermi Telescope have changed our understanding of the most violent objects in the universe.