  We identify a natural way to embed $\mathcal{CP}$ symmetry and its violation
in string theory. The $\mathcal{CP}$ symmetry of the low energy effective
theory is broken by the presence of heavy string modes. $\mathcal{CP}$
violation is the result of an interplay of $\mathcal{CP}$ and flavor symmetry.
$\mathcal{CP}$ violating decays of the heavy modes could originate a
cosmological matter-antimatter asymmetry.
