Plant secondary metabolites, also known as phytochemicals, natural products are unique source for pharmaceuticals, food additives, flavours, industrially important bio-chemicals and responsible for medicinal properties of plants to which they belong. Their classification is based on chemical structure, composition, their solubility in various solvents, or the pathway by which they are synthesized. Four major classes are generally considered; phenolics, terpenes, alkaloids and steroids. Secondary substances have many different functions; of interest in this exercise to their role as chemical signals. Chemical signals act on different levels in a living world. Substances produced by one tissue that influence another tissue within the same organism are hormones. Those produced by one individual and influencing another individual of same species are pheromones. Secondary compounds have no apparent function in a plants primary metabolism but often have an ecological role; they are pollinator attractants, represent chemical adaptations to environmental stresses, or serve as chemical defenses against micro-organisms, insect and higher predators, and even other plant. Secondary metabolites that are used commercially as biologically active compounds (pharmaceuticals, flavors, fragrances and pesticides) are generally higher value lower volume products than the primary metabolites. Thus, secondary metabolites can be considered as special materials and fine chemicals.