any of numerous aromatized and often alcoholic liquids containing bitter substances (chiefly alkaloids, glycosides, or complexes), used as tonics, liqueurs, appetizers, digestives, flavourings, and ingredients to add tang or smoothness to alcoholic drinks. Bitters are prepared according to secret recipes by several manufacturers using bitter herbs, leaves, fruits, seeds, or roots and sometimes alcohol or sugar. The taste is imparted by substances such as orange peel, gentian root, rhubarb root, hop flowers, quassia-wood chips, cascarilla, cinchona bark, and quinine. Aroma is provided by juniper, cinnamon, caraway, anise, nutmeg, camomile, cloves, and other flavouring agents. Bitters are usually named according to the ingredient giving the predominant flavour, such as orange bitters and peach bitters. The alcoholic strength varies but is generally about 40 percent by volume.

Medicinal bitters, few in number and of minor therapeutic value, include compound tinctures of absinthe and of aloes. Early Hebrew history records the addition of sweet-scented or bitter herbs to wine in order to improve and give variety to the flavour. The preparation of aromatic liqueurs originated in France around 1533, and their use spread quickly over the world.