Deltamethrin is a photostable pyrethroid providing valuable insecticidal activity against a large number of pests. Since it has potential uses for crop, cattle, and human health protection, extensive research work was done to evaluate its safety. Protection against insect pests in agriculture requires safety not only for applicators, but also for honey bees, nontarget insects and other arthorpods, mammals and birds in the wild and terrestrial fauna. Protection against vectors of harmful or endemic diseases involves direct treatment of waters with resulting risks for aquatic fauna. Extensive preharvest and postharvest use of a single pesticide demands thorough knowledge of residues on each crop and how they are affected by food processing. These various topics were considered in order to assess the safety of this new insecticide.