This paper defines the basic concepts related to hearing impairment: prenatal, perinatal and postnatal causes of hearing impairment as well as various types of damage according to its degree (deafness or total hearing loss, partial hearing loss). Medical and social model of deafness has been explained. Peculiarities of manual forms of communication have been also given such as manual alphabet, manually coded sign languages which refer to simultaneous character-verbal communication and original sign languages. Data on the structure of the Croatian sign language have been particularly exposed, and the fact emphasized that the sign language has all the components as the spoken language. The most obvious difference is in the way how the signs are produced and perceived. The words in sign language are produced by movements of hands, arms, torso, head and face and are perceived visually. As in a spoken language each word consists of smaller elements, so in the sign language each sign is built of smaller elements: place of articulation, handshape, type of motion, hand orientation and non-manual forms of communication. The signs differ in at least one element (parameter). At the end of the paper is a survey of use of sign language in the world and in Croatia, and it has been established that in the mind of hearing people there are still myths and prejudices about sign languages and deaf people.