A non-nutritive sweetener is a sweetening agent that provides intense sweetness with little or no energy, also called a high-intensity or low-calorie sweetener. The family includes aspartame, sucralose, acesulfame-K, saccharin, steviol glycosides from stevia, and monk fruit extract, each hundreds of times sweeter than sucrose, so tiny amounts replace bulk sugar. They are used in diet soft drinks, sugar-free confectionery, tabletop sweeteners, and increasingly in reformulated mainstream products responding to sugar taxes and reduction targets. All authorised sweeteners undergo extensive safety evaluation with established acceptable daily intakes, though consumer scepticism persists. From a product development view, they bring challenges: different temporal sweetness profiles, bitter or liquorice aftertastes, lack of sugar’s bulking and browning functions, and stability limits in baking or acidic drinks.