  In models where the constants of Nature can take more than one set of values,
the cosmological wave function $\psi$ describes an ensemble of universes with
different values of the constants. The probability distribution for the
constants can be determined with the aid of the `principle of mediocrity' which
asserts that we are a `typical' civilization in this ensemble. I discuss the
implications of this approach for inflationary scenarios, the origin of density
fluctuations, and the cosmological constant.
