The basal ganglia are a richly interconnected set of brain nuclei found in the forebrain and midbrain of mammals, birds, and reptiles. In many species, including most mammals, the forebrain nuclei of the basal ganglia are the most prominent subcortical telencephalic structures. This chapter discusses the general organization of the basal ganglia, covering its neuronal elements, synaptic connections, basic circuit, dendritic membrane properties, and functional operations.