Magnetic fields dominate the universal energy balance on a wide variety of spatial scales; preserving life on Earth from extinction by cosmic rays, regulating star formation in giant molecular clouds, regulating the enrichment of the intergalactic medium by galactic winds and possibly regulating the growth of individual galaxies and filaments of galaxies. The structure of magnetic fields is determined by ubiquitous astrophysical turbulence and critically affects transport processes, including propagation and acceleration of cosmic rays and transfer of heat. Turbulent magnetic fields play an important role in magnetic field generation via dynamo processes, and must be understood to separate galactic foregrounds from the Cosmic Microwave Background signal.