<p>Papaya (Carica papaya L.) is an economically important tropical fruit belonging to the family Caricaceae and is widely consumed because of its pleasant flavour, nutritional value, and traditional medicinal applications. Although the pulp is the principal edible portion, papaya seeds are commonly discarded during fruit consumption and processing. Increasing evidence indicates that papaya seeds are a valuable source of nutrients and biologically active compounds and therefore represent an underutilised plant resource with considerable nutraceutical and food-industry potential. Papaya seeds contain proteins, lipids, dietary fibre, minerals, phenolic compounds, flavonoids, phytosterols, glucosinolates, and isothiocyanate-related compounds. The seed oil is particularly rich in monounsaturated fatty acids, with oleic acid generally being the predominant fatty acid. Experimental studies have reported antioxidant, antimicrobial, anti-inflammatory, antihelminthic, hepatoprotective, hypolipidemic, and other biological activities associated with papaya seed extracts or seed oil. However, much of the evidence remains based on in vitro or animal studies, and results can vary according to cultivar, maturity, extraction method, solvent, dose, and processing conditions. Some constituents of papaya seeds may also have toxicological or reproductive effects at particular doses, emphasising the need for appropriate safety evaluation before therapeutic or concentrated dietary use. This manuscript reviews the nutritional composition, phytochemical constituents, extraction and processing methods, biological activities, food and industrial applications, safety considerations, and future research prospects of papaya seeds. Greater utilisation of papaya seeds could contribute to waste reduction, development of functional foods and nutraceutical ingredients, and improved economic value of papaya processing by-products.</p>