All senses must reckon with the richness of the world, but nothing matches the challenge faced by the olfactory system that underlies our sense of smell. We need only three receptors in our eyes to sense all the colors of the rainbow—that’s because different hues emerge as light-waves that vary across just one dimension, their frequency. The vibrant colorful world, however, pales in comparison to the complexity of the chemical world, with its many millions of odors, each composed of hundreds of molecules, all varying greatly in shape, size and properties. The smell of coffee, for instance, emerges from a combination of more than 200 chemical components, each of which is structurally diverse, and none of which actually smells like coffee on its own. “The olfactory system has to recognize a vast number of molecules with only a few hundred odor receptors or even fewer,” says Rockefeller University neuroscientist Vanessa Ruta (photo), PhD. “It’s clear that it had to evolve a different kind of logic than other sensory systems.” In a new study, Dr. Ruta and her colleagues offer answers to the decades-old question of odor recognition by providing the first-ever molecular views of an olfactory receptor at work.