This chapter provides information on the formation and characteristics of hailstones, hailstorms, and the importance of these characteristics when performing hail damage assessments. It explores the relationships between the size of hail and the dents they produce on metal surfaces. The chapter provides a methodology for the determination of functional/cosmetic damage to roof and exterior finished surfaces and components. The need to understand the full impact of hail damage to buildings and property has been an ongoing topic of concern to both owners and the insurance industry for many years. The formation of hailstones first begins with a hailstone “embryo” or “kernel,” which typically consists of supercooled water freezing on contact with frozen raindrops, ice crystals, dust, or other types of nuclei, which have been drawn into the colder regions of the cloud and serve as a core for the initial growth of the hailstones.