In humans the sense of smell plays an important role in protecting the organism from external hazards like fire, gas or spoiled food, in the consumption of food and in chemical communication with one another. Increasingly, the study of human olfaction is relevant to a number of medical problems connected with olfactory dysfunction, i.e. neurodegenerative diseases which are also manifested in the olfactory epithelium. Although much is known about behavioral aspects and neuronal activities elicited by odorants, we still cannot clearly describe the molecular mechanisms by which odor stimuli are transformed into an electrical cell signal. Here recent progress in our knowledge about the molecular elements of the transduction machinery are reviewed. It can help to understand the general principles underlying our sense of smell.