Global symmetries play a crucial role in quantum field theory, but many
lines of evidence suggest that exact global symmetries are not allowed
in a consistent theory of quantum gravity. As a result, any would-be
global symmetry of a low-energy effective field theory must be either
gauged or broken upon coupling the theory to gravity. In this talk, we
will see how many familiar phenomena from string theory, the AdS/CFT
correspondence, and particle physics can be understood as consequences
of gauging or breaking global symmetries in quantum gravity.