Mercury occurs naturally in the environment and exists in several forms. Elemental mercury, also known as metallic of liquid mercury, is a unique metal that forms a dense, silvery liquid at room temperature. The liquid can disperse and coalesces into small, shiny droplets. These unusual properties attract the interest of children, increasing their propensity to play with mercury. Mercury vapour is readily absorbed by the lungs, making inhalation of elemental mercury the exposure route of greatest concern. The health effects that may result from mercury vary with the magnitude, dose, and duration of exposure. This book examines and identifies the common sources of elemental mercury exposure in children and describes the location, demographics, and proportion of children exposed or potentially exposed to elemental mercury in the United States.