This chapter explains the terms ‘frequency’ and ‘intensity/amplitude’, in providing definitions of hearing impairment and deafness. I look at the prevalence of hearing impairment. After drawing a distinction between sensory-neural deafness and conductive deafness, the chapter considers various causal factors. In discussing the identification and assessment of hearing impairment, I refer to screening risk criteria for congenital or early onset deafness and describe various tests of hearing. The chapter examines implications of hearing impairment, especially those concerning visuospatial skills, short-term memory and cerebral organisation. The family and deaf culture are considered.