  Now that LIGO and Virgo have begun to detect gravitational wave events with
regularity, the field of gravitational wave astronomy is beginning to realise
its promise. Binary black holes and, very recently, binary neutron stars have
been observed, and we are already learning much from them. The future, with
improved sensitivity, more detectors, and detectors like LISA in different
frequency bands, has even more promise to open a completely hidden side of the
Universe to our exploration.
