Publisher Summary Various families of plants possess anti-insect compounds. From the Meliaceae family, insecticide molecules have been isolated, the limonoid azadirachtin obtained from Azadirachta indica or Melia azadirachta (neem) being the most potent and studied. Another tree belonging to the Meliaceae family, far less studied than the previously mentioned, is Melia azedarach. This chapter presents information about the active principles isolated by various investigators from M. azedarach together with their respective bioactivities. Moreover, the chapter describes the effects on feeding, growth, larval and pupal development, fecundity, fertility, toxic effects, as well as alterations in the insect morphology of different extracts.