It is often claimed that Einstein's magnum opus---his 1915 theory of General Relativity---is distinguished from other theories of space and time in virtue of its background independence. It's also often claimed that background independence is an essential feature of any quantum theory of gravity. But are these claims true? This book aspires to offer definitive answers to both of these questions, by (a) charting the space of possible definitions of background independence, and (b) applying ...