Deafness is one of the most widespread, costly and poorly understood disabilities in the world. Hearing impairment is a condition that involves medical, psychological and social aspects. According to the World Health Organization (WHO) about 250 million people have disabling hearing loss and two-thirds of them live in the developing world. Millions of people progressively lose their most important means of communication and became socially isolated, especially in the later years of their life. This handbook provides recent research on several different hearing disorders.