The first steps in the olfactory process occur in the nasal cavity, where an olfactory response, intended to be transmitted to the brain, is generated following the activation of olfactory receptors by odorants. In this context, it has been observed that fine control of the concentration of odorants in the vicinity of the receptors is critical to avoid limitation or saturation of the system. The availability of odorants to receptors is indeed under the control of perireceptor mechanisms, including the enzymatic metabolism of odorants. This chapter will focus on odorant-metabolizing enzymes (OMEs) and will highlight the recent advances that have implicated these enzymes in (i) termination of the olfactory signal and (ii) modulation of the quality of the signal through the synthesis of odorant metabolites as additional olfactory stimuli. The chapter documents the identification, characterization, localization, and function of OMEs in the olfactory mucosa of various mammalian animal models, emphasizing the importance of enzymatic perireceptor mechanisms in olfactory perception.