 QCD does not violate the CP-symmetry as easily as the electroweak theory; unlike the electroweak theory in which the gauge fields couple to parity-violating chiral currents, the gluons of QCD couple to vector currents.The absence of any observed violation of CP-symmetry is a problem because there are natural terms in the QCD Lagrangian that are able to break the CP-symmetry.For a nonzero choice of the ' angle and the chiral quark mass phase ' one expects the CP-symmetry to be violated.