Chemical signals govern a large part of insect behavior and physiology. Within a species chemical communication is mediated by pheromones. Insect pheromones are described briefly, with particular emphasis on sex attractants. Identification of pheromones is presented using the example of an unusual, caffeine-like alkaloid, 1,3-dimethyl-2,4-(1H,3H)-quinazo-linedione, the sex pheromone of the pale-brown chafer, Phyllophertha diversa. Biosynthetic pathways are described for pheromones from the best