After more than 40 years of experimental effort, the gravitational waves predicted by Einstein were finally detected in 2015. Knowledge of stellar mass sized black holes has advanced considerably since then, and plans are already in place to search for emission from the super massive black holes that exist in the centre of galaxies and play a role in the evolution of galactic structure. There is also the possibility of detecting the echoing remnants of the Big Bang itself. What may be discovered over the next few decades as the gravitational sky is explored further?