This paper reviews the characteristics of pheromone and odorant-binding proteins (OBP) in insects, with particular reference to Lepidoptera. They are small (15 kDa) soluble proteins, very concentrated in the lymph of chemosensory sensilla and belonging to two major classes, pheromone-binding proteins (PBP) and general odorant-binding proteins. They represent the insect equivalent of vertebrate OBP. The main unsolved question with OBP of insects and vertebrates regards their physiological role in olfactory transduction. The recent discovery of several types of OBP in the same animal species suggests that these proteins may be involved in the discrimination of odours.