The Madden-Julian Oscillation (MJO) is a dominant component of tropical variability at intraseasonal time scales.The activities of the MJO convection have important impacts on weather and climate systems in many parts of the world.The study of the MJO therefore represents one of the frontiers of atmospheric science.Since the convective initiation is the least understood aspect of MJO,this review aims to synthesize and summarize studies of convective initiation of the MJO include but are not limited to:its observed precursor signals,the numerical simulations,and the mechanisms.The focuses of ongoing research and unsolved issues related to MJO initiation are also presented.