Gravitational wave detectors have been under development since the pioneering work of Weber in the 1960s. The long and painstaking research effort has yielded enormous improvements in detector sensitivity. Astronomical observations of binary pulsar systems have confirmed the existence of gravitational radiation. Direct detection is inevitable once planned detectors reach sensitivity goals.This review begins by introducing the concept of gravitational waves, and discusses their significance. Section 2 discusses sources of gravitational waves, giving estimates of signal characteristics and signal strengths. Section 3 presents an overview of gravitational wave detection and the critical issues of data processing.In the fourth section the physics of resonant-mass gravitational wave detectors is discussed in some detail, covering all areas from antenna materials to transducers and the quantum limits to measurement. This section reviews the major operating antennas in the existing worldwide array but also discusses the prospects for achieving substantial increases in sensitivity in the future.The fifth section presents the concepts and designs for laser interferometer gravitational wave detectors. Large-scale devices will be in operation in the first decade of the twenty-first century and should eventually be certain of detecting a known class of gravitational wave source. At their predicted sensitivity, space interferometers will be able to detect numerous known galactic sources of gravitational waves and also will be able to detect black hole mergers that are thought to have occurred as primordial galaxies merged and grew in the early universe.