Gravitational Waves

This article reviews current efforts and plans for gravitational-wave detection, the gravitational-wave sources that might be detected, and the information that the detectors might extract from the observed waves. Special attention is paid to (i) the LIGO/VIRGO network of earth-based, kilometer-scale laser interferometers, which is now under construction and will operate in the high-frequency band ($1$ to ${10}^4$ Hz), and (ii) a proposed 5-million-kilometer-long Laser Interferometer Space Antenna (LISA), which would fly in heliocentric orbit and operate in the low-frequency band (${10}^{-4}$ to $1$ Hz). LISA would extend the LIGO/VIRGO studies of stellar-mass ($M\sim 2$ to $300M_{\odot }$) black holes into the domain of the massive black holes ($M\sim 1000$ to ${10}^8{M}_{\odot }$) that inhabit galactic nuclei and quasars.