NuSTAR (the Nuclear Spectroscopic Telescope Array) is a NASA Small Explorer mission launched in 2012 and the first telescope in orbit to create images by focussing light in the high-energy X-ray (3 – 79 keV) region of the electromagnetic spectrum. NuSTAR is an active mission dedicated to guest observer programs, including coordination with other X-ray missions and responding to the rapidly changing X-ray sky. Its unique capabilities enable the study of a wide range of scientific targets, from supermassive black holes to our very own Sun.