Recent molecular biological advances have led to a revolution in our understanding of the vomeronasal system’s role in the control of rodent behaviour. This chemosensory system, which is found in most vertebrates, functions in parallel with the main olfactory system and is specialised for the detection of involatile sources of chemosignals, such as skin secretions and territorial marks. Analysis of the mouse genome has revealed a surprisingly rich diversity of vomeronasal receptors with a total of around 260 receptor types, belonging to 3 unrelated gene families1. As yet the ligands for most of these receptors remain to be identified, but the range of known vomeronasal stimuli continues to expand and includes small volatile molecules, peptides and proteins2. These chemosignals convey key social information such as the sex and individual identity of the producer, as well as their endocrine and disease status. Certain behaviours, such as aggressive interactions among male mice, appear to be dependent on vomeronasal sensory input, as they are not observed in animals in which vomeronasal function has been disrupted. Our understanding of how male mouse sexual behaviour is switched to aggressive behaviour in the presence of a potential competitor is far from complete. However, an anatomical basis for this switch may reside in the inhibitory interactions in the neural pathways conveying vomeronasal information about male and female chemosignals, via their projections to hypothalamic areas3. Pheromonal effects on mammalian behaviour are quite variable and are heavily influenced by context and prior experience. Part of this variability arises from the integrated roles of the main olfactory and vomeronasal systems. There are considerable overlaps, both in stimuli that can be sensed by each system and in their projections to the medial amygdala4, which plays a major role in social recognition. Certain involatile components of male mouse urine, most probably major urinary proteins, appear to be innately rewarding, and can support associative learning of volatile odours sensed by the main olfactory system5. This integration of information is likely to occur at the level of the medial amygdala and results in conditioned main olfactory cues reinforcing the behavioural response to vomeronasal stimuli. Learning can also influence responses by gating the transmission of vomeronasal information. Female mice learn to recognise the individual chemosensory signature of their mate during a sensitive period after mating. Formation of this memory is dependent on noradrenergic transmission and appears to be associated with a long-lasting increase in the inhibitory control of mitral/tufted cell projection neurons in the accessory olfactory bulb. This increased gain of granule cell feedback inhibition is proposed to underlie recognition by selectively blocking the transmission of the mate’s chemosensory signal, at the first stage of sensory processing6. Thus the mating male’s chemosignals are less effective in activating downstream neurons in the medial amygdala and arcuate hypothalamus than chemosignals of a male to which the female has been exposed without mating. Interestingly, memory formation is associated with a dramatic and long-lasting increase in the power of local field potential oscillations in the accessory olfactory bulb7. This suggests that learning involves major changes in the oscillatory dynamics of the neural system and that “life events” such as mating can have long-term influences on the physiological and behavioural responses to vomeronasal stimuli.