A bitters is an alcoholic beverage that is flavored with herbal essences and has a bitter or bittersweet flavor. There are numerous brands of bitters that were formerly marketed as patent medicines but are now considered to be digestifs, rather than medicines. They commonly have an alcoholic strength of 45% ABV and are used as digestifs and as flavoring in cocktails.

The word "bitters" derives from the fact that it does not contain added sugar or sweetener despite being strongly flavored. However, if the bitters is a tonic, it may have some added sugar, although European Union legislation defines bitters as having no added sugar.[citation needed]

In the United Kingdom, Angostura bitters are not classified as an alcoholic beverage, and they can be bought by persons of any age.