Sodium Saccharin (benzoic sulfimide) is an artificial sweetener with effectively no food energy. It is about 300–400 times as sweet as sucrose but has a bitter or metallic aftertaste, especially at high concentrations. Saccharin is used to sweeten products such as drinks, candies, cookies, and medicines.

Saccharin derives its name from the word "saccharine", meaning "sugary". The word saccharine is used figuratively, often in a derogative sense, to describe something "unpleasantly over-polite" or "overly sweet". Both words are derived from the Greek word σάκχαρον (sakcharon) meaning "gravel". Related, saccharose is an obsolete name for sucrose (table sugar).

Saccharin is heat stable. It does not react chemically with other food ingredients; as such, it stores well. Blends of saccharin with other sweeteners are often used to compensate for each sweetener's weaknesses and faults. A 10:1 cyclamate:saccharin blend is common in countries where both these sweeteners are legal; in this blend, each sweetener masks the other's off taste. Saccharin is often used with aspartame in diet carbonated soft drinks, so some sweetness remains should the fountain syrup be stored beyond aspartame's relatively short shelf life.

In its acid form, saccharin is not water-soluble. The form used as an artificial sweetener is usually its sodium salt. The calcium salt is also sometimes used, especially by people restricting their dietary sodium intake. Both salts are highly water-soluble: 0.67 g/ml water at room temperature.