  This is a discussion of how we can understand the world-view given to us by
the Everett interpretation of quantum mechanics, and in particular the role
played by the concept of `world'. The view presented is that we are entitled to
use `many-worlds' terminology even if the theory does not specify the worlds in
the formalism; this is defended by means of an extensive analogy with the
concept of an `instant' or moment of time in relativity, with the lack of a
preferred foliation of spacetime being compared with the lack of a preferred
basis in quantum theory. Implications for identity of worlds over time, and for
relativistic quantum mechanics, are discussed.
