The claustrum is an evolutionarily conserved structure, which in mammals, is well connected to most of the neocortex in a topographical manner. The claustrum has thus been deemed an important site for combining sensory information from different modalities, and its widespread projections put this structure in an ideal place to modulate processing in different cortical regions. Yet, our understanding of the properties and function of this structure is rather limited. Using extracellular recordings we map the sensory specific responses and quantify the integration properties of the claustrum of awake monkeys. Using paradigms employing visual, auditory and somatosensory stimuli, we find interactions between the audio-visual and the audio-somatosensory modalities, with the recorded responses exhibiting transient activity specific to the onset of the stimulus. At many sites, the responses to combined stimuli differ from the unisensory responses. Furthermore, comparing sensory responses recorded in the claustrum to those recorded at adjacent multisensory sites in insular cortex and putamen, we find that neurons in the claustrum often respond with much higher firing rates. In addition, we study the anatomical connectivity of the claustrum in the rat. Afferent and efferent projections subdivide this structure into sensory specific regions. Although particular modality specific zones have been shown to overlap, others remain aloof. This challenges the hypothesis that this structure facilitates multi-sensory integration across all modalities. Using anterograde and retrograde tracers we identify intra-claustral projections that connect the different sensory zones. Our results not only confirm previous reports of arealization, but also suggest new routes of multisensory interactions involving this structure. Altogether, our findings well support a role for the claustrum in facilitating the interaction of the different senses.