  We provide a derivation of the Born Rule in the context of the Everett
(Many-Worlds) approach to quantum mechanics. Our argument is based on the idea
of self-locating uncertainty: in the period between the wave function branching
via decoherence and an observer registering the outcome of the measurement,
that observer can know the state of the universe precisely without knowing
which branch they are on. We show that there is a uniquely rational way to
apportion credence in such cases, which leads directly to the Born Rule. Our
analysis generalizes straightforwardly to cases of combined classical and
quantum self-locating uncertainty, as in the cosmological multiverse.
