New neurons are continuously generated in only a few areas of the adult mammalian brain--the olfactory bulb and the dentate gyrus--where they integrate into already functioning circuitry. In these regions, adult neurogenesis adds another dimension of plasticity that complements the classical molecular and cellular mechanisms of plasticity. In this talk, I will present some recent work on the functional contribution of adult-born neurons to the olfactory bulb circuits. Using a multi-scale approach, from the synapse to the behaviour, I will notably describe our recent efforts  to understand the reciprocal link between adult neurogenesis and  olfactory learning and memory.