A sugar substitute, or artificial sweetener, is a food additive which attempts to duplicate the effect of sugar or corn syrup in taste, but often with less food energy.

An important class of sugar substitutes are known as high intensity sweeteners. These are compounds where sweetness is many times that of sucrose; accordingly, much less sweetener is required and energy contribution often negligible. The sensation of sweetness caused by these compounds (the "sweetness profile") is sometimes notably different from sucrose, so they are used in complex mixtures that achieve the most natural sweet sensation.

If the sucrose (or other sugar) replaced has contributed to the texture of the product, then a bulking agent is often also needed. This may be seen in soft drinks such as soda labeled as "diet" or "light" which contain artificial sweeteners and often have notably different mouthfeel; or in table sugar replacements which mix maltodextrins with an intense sweetener to achieve satisfactory texture sensation.

In the United States, five artificially derived sugar substitutes have been approved for use. They are saccharin, aspartame, sucralose, neotame and acesulfame potassium. These compounds are all high intensity sweeteners. There is ongoing controversy whether artificial sweeteners are health risks. Some studies show that they cause disease in laboratory rats.

The majority of sugar substitutes approved for food use are artificially synthesized compounds. However, some natural sugar substitutes are known — including sorbitol and xylitol, which are found in berries, fruit, vegetables and mushrooms. (Although natural, they may be produced synthetically in bulk food production, to lower production costs.) Other natural substitutes are known but are yet to gain official approval for food use.

Another important group of non-sugar sweeteners are the polyols. These are generally less sweet than sucrose, but have similar bulk properties and can be used in a wide range of food products. Sometimes the sweetness profile is 'fine-tuned' with high intensity sweeteners as described above. As with all food products the development of a formulation to replace sucrose is a complex process.