  The method of decoherent histories allows probabilities to be assigned to
sequences of quantum events in systems, such as the universe as a whole, where
there is no external observer to make measurements. This paper applies the
method of decoherent histories to address cosmological questions. Using a
series of simple examples, beginning with the harmonic oscillator, we show that
systems in a stationary state such as an energy eigenstate or thermal state can
exhibit decoherent histories with non-trivial dynamics. We then examine
decoherent histories in a universe that undergoes eternal inflation. Decoherent
histories that assign probabilities to sequences of events in the vicinity of a
timelike geodesic supply a natural cosmological measure. Under reasonable
conditions, such sequences of events do not suffer from the presence of
unlikely statistical fluctuations that mimic reality.
