Pheromones of bark beetles (Coleoptera: Curculionidae: Scolytinae) have been traditionally placed into one of three functional classes: aggregation pheromones, antiaggregation pheromones, and multifunctional pheromones. I describe problems that are encountered when one attempts to classify individual semiochemicals using these categories, and I reevaluate the suitability of the traditional classification system.