Beer is the world's oldest[1] and most widely consumed[2] alcoholic beverage and the third most popular drink overall after water and tea.[3] It is produced by the brewing and fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize (corn), and rice are widely used. Most beer is flavoured with hops, which add bitterness and act as a natural preservative, though other flavourings such as herbs or fruit may occasionally be included.

Some of humanity's earliest known writings refer to the production and distribution of beer: the Code of Hammurabi included laws regulating beer and beer parlours,[4] and "The Hymn to Ninkasi," a prayer to the Mesopotamian goddess of beer, served as both a prayer and as a method of remembering the recipe for beer in a culture with few literate people.[5][6] Today, the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries.

The basics of brewing beer are shared across national and cultural boundaries. Beers are commonly categorized into two main types—the globally popular pale lagers, and the regionally distinct ales,[7] which are further categorised into other varieties such as pale ale, stout and brown ale. The strength of beer is usually around 4% to 6% alcohol by volume (abv.) though may range from less than 1% abv., to over 20% abv. in rare cases.

Beer forms part of the culture of beer-drinking nations and is associated with social traditions such as beer festivals, as well as a rich pub culture involving activities like pub crawling and pub games such as bar billiards.