Postbiotics are bioactive substances generated by bacteria during fermentation, providing unique health advantages beyond those of probiotics and prebiotics. These substances, including enzymes, peptides, short-chain fatty acids (SCFAs), bacteriocins, exopolysaccharides (EPSs), and vitamins, are essential for sustaining human and animal health. Postbiotics influence biological processes by mechanisms including gut microbiota modification, immunomodulation, and anti-inflammatory and antioxidant actions. They promote gastrointestinal (GI) health, regulate metabolism, increase immunological function, and have neuroprotective, antibacterial, and anticancer activities. Postbiotics are used in both the food and pharmaceutical industries, especially in fermented goods and nutritional supplements; nonetheless, issues concerning manufacturing, stability, and regulatory compliance persist. A recent study underscores their involvement with the gut–brain axis and possible synergistic effects with probiotics and prebiotics, paving the way for personalized nutrition and treatment. Moreover, postbiotics are progressively used in veterinary medicine for illness prevention and enhanced animal nutrition, particularly in poultry, aquaculture, and cattle. Technological developments are propelling breakthroughs in postbiotic manufacturing and delivery systems; nonetheless, future studies must tackle safety issues and develop definitive regulatory frameworks. Postbiotics, with their promised therapeutic potential, are poised to significantly influence future health policies, enhancing both preventive and personalized treatment.