The Square Kilometre Array: An international radio telescope for the 21st century

The Square Kilometre Array (SKA) is a next-generation radio telescope which will answer fundamental questions about the origin and evolution of the Universe. With a million square metres of collecting area, the SKA will be 50 times more sensitive than any other telescope ever constructed. Recent technological developments in both computing and radio frequency devices make it feasible to begin construction on such a facility in the next five years. Five key science projects for the SKA have been identified, focused on unsolved problems in fundamental physics, cosmology, galaxy evolution, and planet formation. In addition to answering these and other specific questions, the vast increase in sensitivity provided by the SKA will also almost certainly lead to the discovery of new and totally unexpected celestial phenomena. In this talk, I will review the science that motivates the SKA, will explain the instrumental specifications which result, and will highlight the prototype SKA facilities that are now under construction.