By resorting to results on the Quantum Field Theory of field mixing, showing that the Fock space for the flavor fields is unitarily inequivalent to the one for the unmixed fields, we derive the exact formulas for flavor oscillations, both for bosons and for fermions. These formulas exhibit new features with respect to the usual formulas derived in Quantum Mechanics, which however are reobtained in the relativistic limit. The nature of the QFT corrections is essentially non-perturbative.

We discuss the structure of currents and charges for flavor fields and show that the oscillation formulas have to be derived by use of the flavor Hilbert space. The states for mixed particles are shown to be generalized coherent states. We also study Green's functions for mixed fields and show that the correct propagators cannot be obtained by use of perturbation theory.

We consider both two-flavor neutrino oscillations and meson oscillations. Results on three-flavor neutrino mixing and oscillations are also reported. Some recent topics in this field will be also discussed.