  We briefly overview the historical controversy around Standard Model
predictions of $\varepsilon'/\varepsilon$ 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, $\mathrm{Re}(\varepsilon'/\varepsilon) =
(14\pm 5)\cdot 10^{-4}$, is in excellent agreement with the experimentally
measured value.
