Beer is made from malt, water, hops, and yeast. The malt and water are brought to a boil, hops are added, the "wort" (unfermented beer) is cooled, and yeast is added to cause fermentation. Other ingredients are common in brewing, such as fruit, spices, grains other than the standard barley (such as wheat, rye, and oats), honey, sugar, and anything else that you'd consider ingesting.