  The chiral magnetic effect (CME) in quantum chromodynamics (QCD) refers to a
charge separation (an electric current) of chirality imbalanced quarks
generated along an external strong magnetic field. The chirality imbalance
results from interactions of quarks, under the approximate chiral symmetry
restoration, with metastable local domains of gluon fields of non-zero
topological charges out of QCD vacuum fluctuations. Those local domains violate
the $\mathcal{P}$ and $\mathcal{CP}$ invariance, potentially offering a
solution to the strong $\mathcal{CP}$ problem in explaining the magnitude of
the matter-antimatter asymmetry in today's universe. Relativistic heavy-ion
collisions, with the likely creation of the high energy density quark-gluon
plasma and restoration of the approximate chiral symmetry, and the possibly
long-lived strong magnetic field, provide a unique opportunity to detect the
CME. Early measurements of the CME-induced charge separation in heavy-ion
collisions are dominated by physics backgrounds. Major efforts have been
devoted to eliminate or reduce those backgrounds. We review those efforts, with
a somewhat historical perspective, and focus on the recent innovative
experimental undertakings in the search for the CME in heavy-ion collisions.
