Motor disability is the cardinal symptom of cerebral palsy. Based on the nature of motor dysfunction, cerebral palsy can be subdivided into three major types: 1) spastic cerebral palsy associated with damage to cortical motor areas and/or underlying white matter, 2) choreoathetotic cerebral palsy associated with damage to the basal ganglia, and 3) ataxic cerebral palsy associated with damage to cerebellar structures. People with cerebral palsy often exhibit a wide range of motor symptomatology representing a mix of these three basic conditions. Common motor disorders in cerebral palsy that may appear in different combinations include cocontraction of antagonist muscles, spasticity and related signs such as clonus and reflex irradiation, mirror movements, impaired ability for rapid and selective voluntary activation of muscles, increased muscle tone often appearing as sustained involuntary contractions at rest, chorea, athetosis, dystonia, impaired balance control, and ataxia. This paper focuses on recent neurophysiological developments in understanding the nature of motor impairments in cerebral palsy, particularly with reference to co-contraction of antagonist muscles, mirror movements, and basal ganglia circuit dysfunction that may underlie choreoathetotic disorders.