Dystonia is characterized by sustained contractions of skeletal muscles leading to twisting movements and abnormal postures. It can be a symptom in many disease states (secondary dystonia), but can also occur as an independent entity (primary dystonia). The primary dystonias include more than 15 different single gene syndromes, most of which are inherited as autosomal dominant conditions with reduced penetrance with no neuronal degeneration. Genetic and pharmacological evidence points to basal ganglia circuits as a frequent site of pathology in dystonia. However, human imaging studies show that the CNS circuitry is altered at many levels including the sensorimotor cortex, thalamus, and cerebellum. There are animal models which reproduce the genetics or the phenomenology of human dystonia, although no existing single model reproduces both characteristics. Dystonia may represent a condition of self-reenforcing plasticity in the nervous system in a multilevel network that integrates sensory induced motor control. © 2009 Elsevier Ltd All rights reserved.