Although smells are some of the most evocative and emotionally charged sensory inputs known to us, we still understand relatively little about olfactory processing and odor representation in the brain. This review summarizes physiological results obtained from an insect olfactory system and presents a functional scheme for odor coding that is compatible with data from other animals, including mammals. This coding scheme consists of three main and concurrent odor-induced phenomena: 20-30 Hz oscillatory mass activity; patterned and odor-specific neuronal responses; and transient, dynamic synchronization of odor-specific neural assemblies. When these phenomena are considered together, odors appear to be represented combinatorially by dynamical neural assemblies, defined partly by the transient but stimulus-specific synchronization of their neuronal components.