  The goal of the Laser Interferometric Gravitational-Wave Observatory (LIGO)
is to detect and study gravitational waves of astrophysical origin. Direct
detection of gravitational waves holds the promise of testing general
relativity in the strong-field regime, of providing a new probe of exotic
objects such as black hole and neutron stars, and of uncovering unanticipated
new astrophysics. LIGO, a joint Caltech-MIT project supported by the National
Science Foundation, operates three multi-kilometer interferometers at two
widely separated sites in the United States. These detectors are the result of
decades of worldwide technology development, design, construction, and
commissioning. They are now operating at their design sensitivity, and are
sensitive to gravitational wave strains smaller than 1 part in 1E21. With this
unprecedented sensitivity, the data are being analyzed to detect or place
limits on gravitational waves from a variety of potential astrophysical
sources.
