  We present a formalism for the flavor oscillation of unstable particles that
relies only upon the structure of the time Fourier-transformed two-point
Green's function. We derive exact oscillation probability and integrated
oscillation probability formulae, and verify that our results reproduce the
known results for both neutrino and neutral meson oscillation in the expected
regimes of parameter space. The generality of our approach permits us to
investigate flavor oscillation in exotic parameter regimes, and present the
corresponding oscillation formulae.
