In 2016 the Laser Interferometer Gravitational-wave Observatory (LIGO) announced the first direct detection of gravitational waves; minute distortions in space-time caused by cataclysmic events far away in the universe.  Seven years later, with almost 100 gravitational-wave sources detected to-date and the first-generation facilities now over 20-years old, there is growing momentum towards the next-generation of gravitational-wave observatories.  Projects are underway in Europe, Australia, Japan, India and the US to bring new observatories online. I will talk about the sources of the signals we detected, the physics behind the detectors, and prospects for building a next-gen gravitational-wave observatory known as Cosmic Explorer.