ABSTRACT: Plant Secondary Metabolites (PSM) vary in their constituents and are known to perform diverse ecological functions notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. Constitutive metabolites such as terpenoids, sulphur and nitrogen containing secondary metabolites can act as repellents, deterrents, growth inhibitors or poisons causing mortality in cases of antiherbivore function. However, other metabolites such as indole alkaloids and phenolics can be used by plants to choose adequate partners in order to alter the cost: benefit ratio of mutualism to their advantage. Also plants can /do adapt to extreme stress situations through their constitutive or induced metabolites such as; the UV-B protective function of flavonoids, pesticidal defense of coumarins, reactive oxygen species protection of isoflavonoids and other phenolic compounds. This review on the recent developments on this field provides a synthesis of the Function, Ecology and Evolution of plant secondary metabolites and also increasing the awareness of their integrative role in connecting natural systems. It emphasizes the multiple roles of secondary metabolites in mediating the interactions between plants and other organisms and with their environment at a range of scales of ecological organization.