This chapter outlines some of the major physical and sensory disorders and disabilities which may give rise to special educational needs. This includes organic disorders which primarily affect intellectual development and mobility; hearing and visual impairment; and speech, language and communication disorders. The main characteristics of the various conditions will be described and their incidence and medical treatment noted. The implications for teaching and resourcing are only briefly mentioned; they will be discussed further in Chapter 7, ‘Meeting special needs’.