Abstract: With rising ocean heat content driven by global warming, marine heatwaves (MHWs) as extreme ocean temperature anomalies have exhibited significant increases in frequency, intensity, and duration, posing severe threats to global marine ecosystem stability and health. This paper comprehensively reviews recent domestic and international research to systematically synthesize the evolution of MHWs definitions and classification, driving mechanisms, attribution, and impacts. Through reviewing the evolution of MHWs assessment frameworks, we show that current approaches have advanced beyond early single-SST-threshold criteria to develop multidimensional evaluation systems encompassing intensity classification, spatiotemporal clustering, and comprehensive indices, markedly improving the capability to capture large-scale extreme events. Further analysis of the physical driving mechanisms reveals the regionally varying contributions of atmospheric forcing and internal ocean dynamics, as well as their modulation by large-scale climate modes. Anthropogenic greenhouse gas emissions have been confirmed through attribution as the dominant driver of recent extreme MHWs occurrences, with their probability of occurrence increasing nonlinearly under future warming scenarios. The review also summarizes the widespread ecological impacts of MHWs, including coral bleaching, seagrass meadow degradation, and loss of genetic diversity, alongside the compound effects of MHWs combined with typhoons, hypoxia, and ocean acidification. Finally, addressing the limitation that current research predominantly focuses on the sea surface, we provide a perspective on emerging research frontiers extending from two-dimensional surface to three-dimensional subsurface heatwaves, highlighting integrated deep-ocean observational networks and high-resolution modeling as critical foundations for understanding subsurface heatwave evolution mechanisms and enhancing prediction capabilities.