  In this review I classify the possible ways of CPT violation, and I describe
briefly their phenomenology, in both terrestrial and astrophysical experiments,
including antimatter factories, neutral mesons and neutrinos, and discuss the
various sensitivities. I also pay attention to disentangling genuine
quantum-gravity induced CPT violation from `fake' violation due to ordinary
matter effects. A particularly interesting situation arises when the breaking
of CPT invariance is through unitarity violations, in the sense of the matter
theory being viewed as an effective field theory, entangled with decoherening
quantum gravity ``environments''. In such a case the quantum mechanical CPT
operator is ill defined due to another mathematical theorem, and one has novel
effects associated with CPT Violating modifications of Einstein-Podolsky-Rosen
type correlations of entangled meson states in B and phi meson factories.
