  The long-distance contributions to $K\to 2\pi$ amplitudes can be pinned down,
using well established Chiral Perturbation Theory techniques. The strong
S--wave rescattering of the two final pions generates sizeable chiral loop
corrections, which have an important impact on the direct CP violation ratio
epsilon'/epsilon. Including all large logarithmic corrections, both at short
and long distances, the Standard Model Prediction for this observable is found
to be Re(epsilon'/epsilon) = (1.7\pm 0.9) 10^{-3}, in good agreement with the
most recent experimental measurements. A better estimate of the strange quark
mass could reduce the theoretical uncertainty to 30%.
