Over a billion years ago in a distant galaxy, two black holes merged together. That event produced a violent disturbance in the fabric of spacetime---gravitational waves which propagated throughout the universe. Those waves eventually reached the Earth on September 14, 2015, where they were detected by the twin LIGO detectors. The detection of these waves confirms a key prediction of Einstein's theory of relativity and opens up a new way of "listening" to the universe. I will discuss the meaning of Einstein's description of gravity, the history of LIGO, the challenges that had to be overcome to detect gravitational waves, and some of the details and significance of their detection.