  We present measurements of the time-dependent CP-violation parameters S and C
in B^0 --> eta' K^0 decays. The data sample corresponds to 384 million B Bar
pairs produced by e^+ e^- annihilation at the Y(4S). The results are S = 0.58
+- 0.10 +- 0.03 and C = -0.16 +- 0.07 +- 0.03. We observe mixing-induced CP
violation with a significance of 5.5 standard deviations in this b -> s penguin
dominated mode.
