  Crab cavities have been installed in the KEKB B--Factory rings to compensate
the crossing angle at the collision point and thus increase luminosity. The
beam operation with crab crossing has been done since February 2007. This is
the first experience with such cavities in colliders or storage rings. The crab
cavities have been working without serious issues. While higher specific
luminosity than the geometrical gain has been achieved, further study is
necessary and under way to reach the prediction of simulation.
