The limbic system is the border zone where psychiatry meets neurology. The authors provide a model of limbic function that combines phylogenetic, anatomic, functional, and clinical data to interpret diseases relevant to neuropsychiatry. They provide evidence supporting two major divisions in the limbic system: a paleocortical division with the amygdala and orbitofrontal cortex at its center, and an archicortical division with the hippocampus and cingulate cortex at its center. The implicit integration of affect, drives, and object associations is the function of the paleocortical limbic division; explicit sensory processing, encoding, and attentional control is the function of the archicortical limbic division. The two work in concert to integrate thought, feeling, and action. Understanding their development and organization informs us about how best to care for our patients.