As one of the five basic senses, olfaction provides a unique channel to understand our sensory world and socioemotional experiences. It is phylogenetically old, highly conserved in evolution, and ubiquitously employed in the animal kingdom to communicate identity and motivation. Nevertheless, compared to vision and audition, human olfaction is poorly researched. Here six studies were conducted to probe the sensory properties of human olfactory system and its role in socioemotional communication. Study I examined whether sensory rivalry, as in binocular rivalry, also exists in the olfaction system. Study II looked at the influence of smells on visual perception. Study III tested the effect of chemosensory fearful cues on visual emotional perception. Study IV tested people's ability to detect chemosensory emotional cues and the role of familiarity in their sensitivity to such cues. Study V correlated one's chemosensory ability with his/her emotional capacity to probe the behavioral linkages between human olfaction and emotion. Lastly, Study VI examined the neural correlates of the social nature of natural human body odors by using a group of subjects with various degrees of social anxiety. The results demonstrate that there can be rivalry in olfactory processings between the two nostrils and in the cortex, and olfactory processings interact with visual processings. In addition, olfaction and emotion are closely related to each other. The olfactory system processes the socioemotional information conveyed by natural human body odors, which influences people's behavior and emotional processings, but often without their subjective awareness.