This chapter provides the basics of hearing loss, hearing aids and the related special test methods. A number of specific applications of sensory methods are given. Hearing loss is a handicap that seriously affects the quality of life for the individual. For severe hearing losses, speech intelligibility is the highest priority, but for moderate and mild losses sound quality plays an important role for the acceptance of the device and the resulting quality of life. A very important inclusion/exclusion criterion is the nature of the hearing loss. The hearing aid experience is important as it sets a reference for the sound that the listener is exposed to in daily life. The combination of hearing loss criteria, hearing aid experience and cognitive function leads to a sparser pool of potential subjects. The sensory evaluation of sound has a different meaning for hearing impaired listeners than for normal hearing listeners.