The Spitzer view of the extragalactic universe.

The Spitzer Space Telescope was launched in August 2003. Scientists from around the world have applied its orders-of-magnitude gain in imaging and spectroscopic capability to a wide array of topics in extragalactic research. Spitzer studies have found massive galaxies at redshifts greater than 6, resolved the cosmic background at 200 μm > λ > 20 μm into the dusty infrared-luminous galaxies that comprise it, directly detected dust-enshrouded star formation, and measured the star formation history of the universe to z > 3. In this review we examine a small fraction of the extragalactic studies from Spitzer that have been conducted in its first three years of operations.