<p>Noni (<i>Morinda citrifolia</i> L.) has gained widespread attention because of its rich bioactive compounds and multifaceted health benefits. This review comprehensively summarizes the main bioactive components of noni fruit, including iridoids (e.g., deacetylasperulosidic acid, asperulosidic acid, and asperuloside), anthraquinones (e.g., damnacanthal, rubiadin, and alizarin), xeronine (a historically proposed but experimentally unverified alkaloid), and other compounds such as phenolic acids, flavonoids, and scopoletin, along with their physiological activities, including anti-cancer, anti-inflammatory, antioxidant, antibacterial, and immunomodulatory effects, as demonstrated in <i>in vitro</i><i>, </i><i>in vivo</i>, and limited human studies. Fermentation is highlighted as an important processing approach that modifies the microbial composition of noni and has been reported to enhance the stability and bioavailability of its bioactive components, although direct human bioavailability data remain limited. Available toxicological and clinical evidence suggests that noni and its bioactive compounds are generally considered safe within normal dietary intake levels, although long-term human safety data remain limited. This review provides a comprehensive understanding of the chemical characteristics, physiological activities, and fermentation-mediated transformations of noni, offering insights for future development of functional foods and therapeutic applications.</p> Graphical abstract <p></p>