Ion channels are membrane-bound proteins that perform key functions in virtually all human cells. Such channels are critically important for the normal function of the excitable tissues of the nervous system, such as muscle and brain. Until relatively recently it was considered that dysfunction of ion channels in the nervous system would be incompatible with life. However, an increasing number of human diseases associated with dysfunctional ion channels are now recognised. Such neurological channelopathies are frequently genetically determined but may also arise through autoimmune mechanisms. In this article clinical, genetic, immunological, and electrophysiological aspects of this expanding group of neurological disorders are reviewed. Clinical situations in which a neurological channelopathy should enter into the differential diagnosis are highlighted. Some practical guidance on how to investigate and treat this complex group of disorders is also included.