Functional foods are an important innovation in modern nutrition, bridging the health and diet gap by providing physiological benefit alongside fundamental nutrition. This chapter addresses the varied roles of functional foods in health maintenance, chronic disease prevention and management, and sustainable food systems maintenance. Remarkable categories such as probiotics, prebiotics, omega-3 fatty acids, bioactive peptides, polyphenols, and dietary fibers are examined for their potential to improve gut health, augment immune functions, modulate metabolic processes, and reduce the risk of cardiovascular disease, obesity, diabetes, and cancer. Case studies focus on application-oriented solutions, including omega-3-enriched milk products, functional grain and berry for metabolic health, and algae-based supplementations in green aquaculture, to establish the transfer of scientific innovation to practice application. The chapter also focuses on sustainability, and through circular economic approaches such as valorization of food processing by-products into functional ingredients, thereby minimizing environmental footprints while maximizing nutrition content. Today’s trends are also discussed, such as ideas of personalized nutrition based on genetic and microbiome data, and biotechnological advances that enhance the nutrient value of foods using genetically modified crops and precision fermentation. Issues remain with regulation, consumer education, and clinical evidence, yet functional foods have become more established as vital aids in preventive medicine and sustainable nutrition. In short, the chapter demonstrates that functional foods are of immense potential for addressing world health issues as well as environmental problems and therefore are the backbone of food and nutrition policy of the future.