Hops are the flowers (also called seed cones or strobiles) of the hop plant Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though they are also used for various purposes in other beverages and herbal medicine.

In the Middle Ages, beers tended to be of a very low alcohol content (small beer). In Europe, many villages had one or more small breweries with a barley field and a hop garden in close vicinity. Early documents include mention of a hop garden in the will of Charlemagne's father, Pepin III. However, the first documented use of hops in beer is from the 9th century, though Hildegard of Bingen, 300 years later, is often cited as the earliest documented source. Before this period, brewers used "gruit", composed of a wide variety of bitter herbs and flowers, including dandelion, burdock root, marigold, horehound (the old German name for horehound, Berghopfen, means "mountain hops"), ground ivy, and heather.