  In this review we first discuss the string theoretical motivations for
induced decoherence and deviations from ordinary quantum-mechanical behaviour;
this leads to intrinsic CPT violation in the context of an extended class of
quantum-gravity models. We then proceed to a description ofprecision tests of
CPT symmetry and quantum mechanics using mainly neutral kaons and neutrinos. We
also emphasize the possibly unique role of neutral meson factories in providing
specific tests of models where the quantum-mechanical CPT operator is not
well-defined, leading to modifications of Einstein-Podolsky-Rosen particle
correlators. Finally, we discuss experimental probes of decoherence in a
cosmological context, including studies of dissipative relaxation models of
dark energy in the context of non-critical (non-equilibrium) string theory and
the associated modifications of the Boltzmann equation for the evolution of
species abundances.
