Our understanding of gravity has developed rapidly over the past century. This began with Einstein’s revolutionary new theory and continued with sustained developments in our understanding of both the mathematics and the observations that can be used to probe it. I’ve outlined how new gravitational efects have been predicted and observed in the Solar System; in exotic astrophysical systems; and in the Universe as a whole. While I’ve attempted to give some idea of the elegance of the concepts involved, and the details of the wondrous physics that results, this book must inevitably be left incomplete. It is only a very short introduction to the subject. To understand the full profundity of what Einstein achieved, and the beauty of the theory that resulted, there is no alternative but to delve deeper into the maths and physics. This should be a rewarding experience, as Einstein’s theory of gravity lets us understand space and time as they really are. It lets us imagine universes that never were, as well comprehend the one in which we live. It lets us calculate what happens in environments so alien and exotic that our everyday understanding of reality is turned entirely on its head. Yet it is almost certainly incomplete. The final words on gravity have yet to be written.