  Relativistic heavy-ion collisions provide an ideal environment to study the
emergent phenomena in quantum chromodynamics (QCD). The chiral magnetic effect
(CME) is one of the most interesting, arising from the topological charge
fluctuations of QCD vacua, immersed in a strong magnetic field. Since the first
measurement nearly a decade ago of the possibly CME-induced charge correlation,
extensive studies have been devoted to background contributions to those
measurements. Many new ideas and techniques have been developed to reduce or
eliminate the backgrounds. This article reviews these developments and the
overall progress in the search for the CME.
