A cocktail is a style of mixed drink. A cocktail usually contains one or more types of liquor and flavorings, usually one or more of a liqueur, fruit, sauce, honey, milk or cream, spices, etc.

The cocktail became popular during Prohibition in the United States primarily to mask the taste of bootlegged alcohol. The bartenders at a speakeasy would mix it with other ingredients, both alcoholic and non-alcoholic. One of the oldest known cocktails, the Cognac-based Sazerac, dates from 1850s New Orleans, as many as 70 years prior to the Prohibition era.

Until the 1970s, cocktails were made predominantly with gin, whiskey or rum, and less commonly vodka. From the 1970s on, the popularity of vodka increased dramatically. By the 1980s it was the predominant base for mixed drinks. Many cocktails traditionally made with gin, such as the gimlet, or the martini, may now be served by default with vodka.

Carbonated beverages that are used nearly exclusively in cocktails include soda water, tonic water and seltzer. Liqueurs are also common cocktail ingredients.

The earliest known printed use of the word "cocktail," as originally determined by Dr. David Wondrich in October 2005, was from "The Farmer's Cabinet", April 28, 1803.

The second earliest and officially recognised known printed use of the word "cocktail" (and the most well-known) was in the May 13, 1806 edition of the Balance and Columbian Repository, a publication in Hudson, New York , where the paper provided the following answer to what a cocktail was:

"Cocktail is a stimulating liquor composed of spirits of any kind, sugar, water, and bitters--it is vulgarly called a bittered sling and is supposed to be an excellent electioneering potion, inasmuch as it renders the heart stout and bold, at the same time that it fuddles the head. It is said, also to be of great use to a Democratic candidate: because a person, having swallowed a glass of it, is ready to swallow anything else."
The first publication of a bartenders' guide which included cocktail recipes was in 1862: How to Mix Drinks; or, The Bon Vivant's Companion, by Professor Jerry Thomas. In addition to listings of recipes for Punches, Sours, Slings, Cobblers, Shrubs, Toddies, Flips, and a variety of other types of mixed drinks were 10 recipes for drinks referred to as "Cocktails". A key ingredient which differentiated "cocktails" from other drinks in this compendium was the use of bitters as an ingredient, although it is not to be seen in very many modern cocktail recipes.

During Prohibition in the United States (1919-1933), when alcohol possession was illegal, cocktails were still consumed in establishments known as speakeasies. The quality of the alcohol available was far lower than was previously used, and bartenders generally put forth less effort in preparing the cocktails.