Publisher Summary This chapter discusses audiometry and describes the methods required for measuring hearing loss. Hearing can be damaged in many different ways and by a number of agents. Audiometry provides a means of investigating the extent and the nature of the damage. The particular pattern recorded is indicative of the site of damage and of possible causes. The characteristic pattern for noise-induced hearing loss (NIHL) is readily identifiable, where noise is the only damaging agent; however, confusion may arise where other types of hearing damage coexist. It is therefore useful to recognize and be aware of other causes of impaired hearing. The hearing mechanism comprises three distinct parts—the outer ear, the middle ear, and the inner ear. Audiometry is not a substitute for noise control. However, it can be complementary to other activities aimed at protecting hearing. An audiogram is used as legal evidence to prove or deny the existence of NIHL and to quantify it. A prudent employer regularly tests those at risk, taking preventive action at the first sign of NIHL and ensuring that the condition never develops.