We review a proposal of how to complete non-relativistic Quantum Mechanics to a physically meaningful, mathematically precise and logically coherent theory. This proposal has been dubbed \textit{ETH - Approach} to Quantum Mechanics, "E" standing for "Events," "T" for "Trees," and "H" for "Histories." The ETH-Approach supplies the last one of three pillars Quantum Mechanics can be constructed upon in such a way that its foundations are solid and stable. Two of these pillars are well known. The third one has been proposed quite recently; it implies a general non-linear stochastic \textit{law} for the time-evolution of states of \textit{individual} physical systems.
We illustrate the general ideas and results by sketching an application to the quantum theory of \textit{fluorescence} of an atom coupled to the radiation field (in a limit where the velocity of light tends to \infty).
