Publisher Summary This chapter provides an overview of the corpus striatum. The major functional division of the corpus striatum is phylogenetic. The striatum is the receptive region of the corpus striatum. Most striatal efferents are striatopallidal, myelinated fibers passing to the globus pallidus. Striatonigral fibers carry inhibitory γ-aminobutyric acid neurotransmitter to the substantia nigra. Although, there are reciprocal connections between striatum and substantia nigra, their main neurotransmitters are different. As the main efferent component of the corpus striatum, the globus pallidus receives most of the striatal output. The globus pallidus also has reciprocal connections with the subthalamic nucleus. The corpus striatum and cerebellum influence descending pathways via this thalamocortical projection. In the absence of movement, the corpus striatum exerts an inhibitory influence on the thalamus. The diseases of the basal ganglia cause changes in muscle tone and the occurrence of abnormal involuntary movements that are collectively termed dyskinesia.