  The standard theory of neutrino oscillations is reviewed, highlighting the
main assumptions: the definition of the flavor states, the equal-momentum
assumption and the time = distance assumption. It is shown that the standard
flavor states are correct approximations of the states that describe neutrinos
in oscillation experiments. The equal-momentum assumption is shown to be
unnecessary for the derivation of the oscillation probability. The time =
distance assumption derives from the wave-packet character of the propagating
neutrinos. We present a simple quantum-mechanical wave-packet model which
allows us to describe the coherence and localization of neutrino oscillations.
