The NuSTAR mission will deploy the first focusing telescope for imaging the sky with high-energy X-rays. NuSTAR will undertake the first census of supermassive black holes throughout cosmic space and time, map supernova explosions, and study the most extreme active galaxies. The telescope will allow scientists to explore fundamental questions about the universe, such as what happens at the edge of a black hole, the nature of the mysterious "dark energy" pulling apart the universe, and what powered the Big Bang.