What role do hops play in beer brewing?

In the brewing of beer, hops—specifically the dried female flower cones of the common hop—serve several essential functions.12

When boiled in wort, hops contribute the following:

• Flavor and Aroma: Hops contain bitter resins and essential oils that provide beer with its characteristic mellow bitterness and delicate aroma.1
• Chemical Bitterness: The primary compounds responsible for bitterness are humulones. During the boiling process, $\alpha$-acids are isomerized by heat into iso-$\alpha$-acids, which create the distinct bitter flavor profile of the finished beverage.2
• Preservation: The constituents extracted from the hop cones aid in the preservation of the beer.1

Brewers may use whole dried cones, powdered compressed hops, or extracts derived via solvents like carbon dioxide to achieve these qualities.2