This chapter focuses on chemical communication, including olfaction and gustation, plays a central role in structuring primate social relationships, including 'microsmatic' Old World species including humans. Chemical communication is a widespread mechanism used by most living species, including human and non-human primates, incorrectly considered as 'microsmatic' species. It is also a language that can be decoded in the absence of light and, as such, constitutes a prime mode of communication in nocturnal species. The vomeronasal organ (VNO) is specialized in sensing fluidphase molecules, particularly non-volatile odors such as pheromones, thought to mediate reproductive activity. Genes of the major histocompatibility complex called Human Leucocyte Antigens (HLA), in humans illustrate the genetic basis of similarities between olfactory phenotypes. These HLA genes are involved in the immunological response to pathogens, they are highly polymorphic and, therefore, constitute potential markers of olfactory individuality.