  For the neutron to have an electric dipole moment (EDM), the theory of nature
must have T, or equivalently CP, violation. Neutron EDM is a very good probe of
novel CP violation in beyond the standard model physics. To leverage the
connection between measured neutron EDM and novel mechanism of CP violation,
one requires the calculation of matrix elements for CP violating operators, for
which lattice QCD provides a first principle method. In this paper, we review
the status of recent lattice QCD calculations of the contributions of the QCD
$\Theta$-term, the quark EDM term, and the quark chromo-EDM term to the neutron
EDM.
