  We have compared the decay rates of K_L and K_S to \pi^+ \pi^- and \pi^0
\pi^0 final states using a subset of the data from the KTeV experiment (E832)
at Fermilab. We find that the direct-CP-violation parameter
Re(\epsilon'/\epsilon) is equal to (28.0 \pm 3.0 (stat) \pm 2.8 (syst)) \times
10^{-4}. This result definitively establishes the existence of CP violation in
a decay process.
