  Quark interactions with topological gluon fields in QCD can yield local
$\mathcal{P}$ and $\mathcal{CP}$ violations which could explain the
matter-antimatter asymmetry in our universe. Effects of $\mathcal{P}$ and
$\mathcal{CP}$ violations can result in charge separation under a strong
magnetic field, a phenomenon called the chiral magnetic effect (CME).
Experimental measurements of the CME-induced charge separation in heavy-ion
collisions are dominated by physics backgrounds. Major theoretical and
experimental efforts have been devoted to eliminating or reducing those
backgrounds. We review the current status of these efforts in the search for
the CME in heavy-ion collisions.
