This chapter summarizes the functional–anatomic organization of the connectivity of the basal ganglia with the thalamocortical systems and the brainstem. This connectional organization substantiates the neural basis for the wide array of functions in which the basal ganglia are involved, ranging from pure sensorimotor to cognitive–executive and emotional–motivational behaviors. Across this broad array of motor and behavioral functions, the mechanism by which the basal ganglia contribute to these functions is through “response selection.” This mechanism fits well with the arrangement of the intrinsic connections between the individual basal ganglia nuclei, supporting the selection of appropriate responses in a particular context and, at the same time, the suppression of inadequate responses. A variety of symptoms as part of neurologic movement disorders, such as Parkinson’s disease, Huntington’s disease and dystonia, or neuropsychiatric diseases like obsessive-compulsive disorder, mood disorders, and drug addiction, might be interpreted as an inadequate selection of motor, cognitive, or affective responses to internal or external stimuli.