Beer is an alcoholic drink made by fermenting grains, usually barley, with water, hops, and yeast. It's one of the oldest beverages humans have created, with evidence of beer-making dating back thousands of years to ancient Mesopotamia and Egypt.

The brewing process works through fermentation: yeast (a tiny living organism) eats the sugars from the grains and produces alcohol and carbon dioxide as byproducts. The hops, which come from cone-shaped flowers, add bitterness and help preserve the beer. Different techniques and ingredients create different styles: light lagers, dark stouts, fruity ales, and many other varieties.

Throughout history, beer has been important in many cultures. Medieval monks brewed beer in monasteries, and the Pilgrims brought beer on the Mayflower because it was less likely to spoil than water on long voyages.

Today, beer is made in breweries ranging from massive factories to small craft operations. Because beer contains alcohol, it's regulated by law. In the United States, adults must be 21 years old to purchase or drink beer legally.