Root beer is a sweet North American soft drink that is traditionally made using the root bark of the sassafras tree Sassafras albidum or the vine of Smilax ornata (known as sarsaparilla, also used to make a soft drink, sarsaparilla) as the primary flavor. Root beer is typically, but not exclusively, non-alcoholic, caffeine-free, sweet, and carbonated. Like cola, it usually has a thick and foamy head. A common use is to add vanilla ice cream to make a root beer float.

While no standard recipe exists, the primary ingredients in modern root beer are filtered water, sugar, and safrole-free sassafras extract, which complements other flavors. Common flavorings are vanilla, caramel, wintergreen, black cherry bark, licorice root, sarsaparilla root, nutmeg, acacia, anise, molasses, cinnamon, sweet birch, and honey. Soybean protein or yucca are sometimes used to create a foamy quality, and caramel coloring is used to make the beverage brown.

Root beer was originally made with sassafras root and bark which, due to its mucilaginous properties, formed a natural, long-lasting foam, a characteristic feature of the beverage. Root beer was originally carbonated by fermentation. As demand and technology changed, carbonated water was used. Some manufacturers used small amounts of starch (e.g. from cassava) with natural surfactants to reproduce the familiar foaming character of sassafras-based root beer.

Ingredients in early and traditional root beers include allspice, birch bark, coriander, juniper, ginger, wintergreen, hops, burdock root, dandelion root, spikenard, pipsissewa, guaiacum chips, sarsaparilla, spicewood, wild cherry bark, etc. .

Root beer is heavily ingrained in American culture, becoming prominent in the 19th century, having been sold in stores since the 1840s and recipes documented since the 1860s. Some describe root beer as an ‘adulterated sarsaparilla’ because it contains a mix of flavor-enhancing ingredients. Most brewers choose to add vanilla, wintergreen, licorice root, nutmeg, acacia, anise, molasses, cinnamon, clove, or honey to their recipes.