Hops plants were mentioned by the Roman writer Pliny in the first century A.D. as a popular garden plant and vegetable whose young spring shoots were sold in markets and eaten like asparagus.
Hops also serve as a natural preservative, helping to prevent spoilage in beer. Hops comes as either whole flowers or compressed pellets (think rabbit food). There are many varieties of hops available to homebrewers, allowing for great diversity of flavors and aromas.
Different hops are used to brew different styles of beer. For example, cascade hops give American pale ales their distinct citrusy quality, fuggles have an earthiness common in English-style ales, and saaz lend the spicy/herbal character found in European Pilsners.