This chapter discusses limbic system, which is the most advanced part of the primitive brain which encircles the corpus callosum and brainstem like a belt. The limbic system has very low anatomical visibility in the primate brain. Limbic system is a link between the brainstem and the neocortex, where projections from the limbic structures back to the cortex explain how emotions reach consciousness. Medial forebrain bundle is a major efferent connection of the limbic system, and projects from a large number of limbic structures to the hypothalamus, and from there to the reticular formation. Amygdla projects to other regions of the limbic system by means of stria terminalis and the ventral amygdalofugal pathway. The limbic cortex receives projections from the sensory cortex and sends efferents to various neocortical areas, including the prefrontal cortex. Hypothalamus and limbic projections to the reticular formation play an important role in producing the external manifestations of emotion.