The \(\varepsilon '/\varepsilon \)-story: 1976–2021

The ratio $\epsilon'/\epsilon$ measures the size of direct CP violation in $K_L\to\pi\pi$ decays $(\epsilon^\prime)$ relative to indirect one described by $\epsilon$ and is very sensitive new sources violation. As such it played a prominent role particle physics already for 45 years. Due smallness its measurement required heroic efforts 1980s 1990s on both sides Atlantic with final results presented NA48 KTeV collaborations 20 years ago. Unfortunately, even after first calculation we do not know which degree Standard Model agrees this data how large room left contributions ratio. This due significant non-perturbative (hadronic) uncertainties accompanied partial cancellation between QCD penguin electroweak contributions. While control over short distance perturbative effects has been achieved early 1990s, several improvements since then, different views have expressed authors last thirty In fact today uncertainty NP significant. My own work started 1983 involved calculations. writing non-technical recollection steps led present status including historical remarks known everybody. $\Delta I=1/2$ rule also summarized. story dedicated Jean-Marc Gerard occasion 35th anniversary our collaboration his 64th birthday.