Theoretical status of ${\epsilon }^{\mathrm{\prime }}\mathrm{/}\epsilon$

We briefly overview the historical controversy around Standard Model predictions of ${\epsilon }^{\mathrm{\prime }}\mathrm{/}\epsilon$ and clarify the underlying physics. A full update of this important observable is presented, with all known short- and long-distance contributions, including isospin-breaking corrections. The current Standard Model prediction, $$\mathrm{R}\mathrm{e}$(\varepsilon’/\varepsilon) = (14\pm 5)\cdot 10^{-4}$, is in excellent agreement with the experimentally measured value.