Ion cyclotron emission (ICE) is a commonly observed feature of magnetized toroidal plasmas in the presence of fast ions. It is generally agreed that this emission is caused by a strongly inverted (in the velocity space) population of confined fast ions originating from either neutral beam injection (NBI), fusion reactions, or acceleration by waves in the ion cyclotron range-of frequencies (ICRF). As a result, ICE signals can ultimately provide a non-perturbing measure of the state of confined alpha particles in a deuterium-tritium burning fusion reactor, such as ITER or DEMO.