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The afterglow from the Big Bang, called the "cosmic microwave background radiation," serves as the backlight in a shadow theater where galaxies are the actors. The structure of galaxies is still mysterious despite ever-improving telescope observations, because many of their components – including dark matter and diffuse gas ­– are invisible in ordinary light. But we can indirectly detect these features by observing the shadows that galaxies cast on the cosmic microwave background radiation. The shadows  provide clues to how galaxies form and evolve, and help us to work out the nature of dark matter and dark energy in the universe. I will describe the efforts led by SLAC scientists to reveal these galaxy silhouettes, using cosmic microwave background experiments and galaxy surveys of unprecedented scale.