  In the centenary year of Einstein's General Theory of Relativity, this paper
reviews the current status of gravitational wave astronomy across a spectrum
which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper
reviews the historical development of gravitational wave astronomy from
Einstein's first prediction to our current understanding the spectrum. It is
shown that detection of signals in the audio frequency spectrum can be expected
very soon, and that a north-south pair of next generation detectors would
provide large scientific benefits. Sect. 2 reviews the theory of gravitational
waves and the principles of detection using laser interferometry. The state of
the art Advanced LIGO detectors are then described. These detectors have a high
chance of detecting the first events in the near future. Sect. 3 reviews the
KAGRA detector currently under development in Japan, which will be the first
laser interferometer detector to use cryogenic test masses. Sect. 4 of this
paper reviews gravitational wave detection in the nanohertz frequency band
using the technique of pulsar timing. Sect. 5 reviews the status of
gravitational wave detection in the attohertz frequency band, detectable in the
polarisation of the cosmic microwave background, and discusses the prospects
for detection of primordial waves from the big bang. The techniques described
in sects. 1-5 have already placed significant limits on the strength of
gravitational wave sources. Sects. 6 and 7 review ambitious plans for future
space based gravitational wave detectors in the millihertz frequency band.
Sect. 6 presents a roadmap for development of space based gravitational wave
detectors by China while sect. 7 discusses a key enabling technology for space
interferometry known as time delay interferometry.
