The existence of gravitational waves is the most prominent of Einstein's predictions that has not yet been directly verified. The space project LISA shares its goal and principle of operation with the ground-based interferometers currently under construction: the detection and measurement of gravitational waves by laser interferometry. Only in space, detection of signals below, say, 1 Hz is possible. LISA, a joint project of ESA and NASA, is a mission that will measure these low-frequency waves. LISA consists of three spacecraft in heliocentric orbits, forming a triangle with 5 million km sides. Launch for LISA is scheduled for 2011, following a technology demonstrator LTP in 2006.