Abstract: Marine biofouling presents a persistent and formidable challenge for ocean-going vessels and marine engineering throughout their service life. Over time, the submerged surfaces of ship hulls and offshore structures become highly susceptible to colonization by marine organisms such as barnacles, mussels, and algae, leading to the formation of typical biofouling communities. This type of fouling not only significantly increases hydrodynamic drag and fuel consumption, but also accelerates the corrosion and degradation of structures, resulting in substantial economic losses for the global shipping industry. Itis estimated that biofouling causes direct economic loss exceeding 12 billion annually worldwide, and also posing potential environmental risks to marine ecosystems. To address these issues, the development of efficient and environmentally friendly marine antifouling coatings has become a research hotspot in the field of marine engineering. In the antifouling coating systems, antifouling agents, serving as the key functional components, play a decisive role in determining the coatings’ antifouling performances and service life. In this study, the types, mechanisms of action, and current applications of the major commercial antifouling agents are reviewed. The latest research advances in emerging antifouling agents, such as those derived from the carbon quantum dot, nanomaterials, and natural products are particular emphasized, and their antifouling mechanisms and application potential are thoroughly analyzed, with the aim of offering theoretical guidance and technical references for the selection of antifouling agents and the development of novel marine antifouling coatings.