The Laser Interferometer Space Antenna (LISA) is the first instrument to directly measure gravitational waves propagating through space. The mission, a joint effort of NASA and the European Space Agency, consists of three identical spacecraft trailing Earth in a triangular formation. Laser beams will measure changes of a few trillionths of a meter in the distance between the craft, induced by the passing of gravitational waves from distant events such as black-hole mergers. Such detections will provide an important test of Einstein?s theory of general relativity. A predecessor to LISA, LISA Pathfinder, is slated to launch in 2011 to test technology required for the success of the later mission, which will launch no earlier than 2020.