Review on epsilon'/epsilon

Experiments at CERN and Fermilab have been competing each other to improve the measurement of a CP violation parameter, epsilon'/epsilon. Fermilab KTeV-E832 recently announced their final result, Re(epsilon'/epsilon) = [19.2 +- 2.1] x 10^{-4}. The new world average shows the existence of direct CP violation in the decay process itself with 12 standard deviations.