Radiation from all galaxies that ever existed suffuses the universe with a diffuse extragalactic background light (EBL). Measuring the EBL is as fundamental to cosmology as measuring heat from the Big Bang (cosmic microwave background) at radio wavelengths. Researchers describe the best measurement yet of the evolution of the EBL over the past 5 billion years, based on observations from radio waves to gamma rays from NASA spacecraft and ground-based telescopes.