Beer is the world's oldest and most widely consumed alcoholic beverage and the third most popular drink overall after water and tea. 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 flavored with hops, which adds bitterness and acts as a natural preservative, though other flavorings such as herbs or fruit may occasionally be included.

Some of humanity's earliest known writings refer to the production and distribution of beer Today the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brew pubs 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, which are further categorized 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.