All hearing aids must be managed and maintained to obtain the best from them. They need to be free from feedback (whistling), distortion and unwanted noise. Simple daily checks should be carried out on all systems, with regular more detailed testing to ensure they are working well and up to specification. This chapter considers the maintenance of some of the common hearing aid systems. The guidance given here is of a general nature and much of what is written can be applied to other systems not specified in this chapter.