The Big Bang Observer (BBO) is a proposed successor to the Laser Interferometer Space Antenna (LISA). The primary scientific goal will be the observation of gravitational waves from the time shortly after the Big Bang, but it will also be able to detect younger sources of gravitational radiation, like binary inspirals. BBO will likely be sensitive to all LIGO and LISA sources, and others. Its extreme sensitivity comes from the higher-power lasers, and correlation of signals from several different interferometers located around the Sun.