Animals benefit from a number of sensory tools that allow them to perceive the world, and thus to interact adequately with this latter. In a large number of mammalian species, one of these senses, olfaction, if particularly developed. This sense allows the perception of millions of different stimuli and to extract information from them, without prior experience of these molecules. This remarkable ability is based on the expression of specific odorant receptors by sensory neurons located in the nasal cavity. The genes coding for these receptors are numerous (over 1500 in the mouse) and variable. Each neuron expresses a single of these genes, providing to each sensory cell a defined and limited functionality. All axonal projections emanating from neurons that express the same odorant receptor gene converge in the olfactory bulb, forming spherical structures called glomeruli.