|Gravitational-waves, a consequence of the theory of general relativity, are ripples in the fabric of space-time itself. Only the most violent processes in the Universe can generate gravitational-waves of a strength that will make their detection feasible. Among these events are the collisions of black holes or neutron stars, as well as supernova explosions. Gravitational-wave detection might eventually also shed light on matter and processes that do not interact with electro-magnetic waves at all, i.e. dark matter may be able to become directly observable. Thus, the detection of gravitational-waves will open a new and complementary window to the universe, through which these processes will be made visible. While the first generation of gravitational-wave detectors did not yet find these waves, the coming generation of detectors, including KAGRA in Japan, is anticipated to make regular detections.