Host and site-related stimuli and pheromones have long been known to aggregate or attract arthropod vectors of filth and disease. The exploitation of these semiochemicals for monitoring largely has been confined to carbon dioxide-baited traps. However, there is a great deal of recent activity to expand the arsenal of chemicals and to understand the nature of some that are long known. These efforts are intended to develop improved systems for control of major disease problems. In addition, there has been a major commercial expansion of semiochemical-based products, particularly those aimed at the household market.