This chapter discusses the origin of the oligosaccharin concept, preparation of oligosaccharins, bioassays, and explains the purification and chemical characterization of oligosaccharides. The physiology of oligosaccharin effects is discussed in detail and the mode of action of oligosaccharins is described. The rapid effects of oligosaccharins and the direct effects of oligosaccharides on enzymes are covered. Various techniques have been developed to study the natural occurrence of oligosaccharides. The processes of formation of oligosaccharides by means of solubilizing and degradation by converting them to monosaccharaides are described. Chitins' role as defense receptor and glucanases role to damage to cell wall are also discussed. The chapter also covers the movements of oligosaccharides in plants. Some large and hydrophilic molecules cannot penetrate whereas some move down till the auxiliary buds to carry out their biological actions. The movement of pectic oligosaccharides and their active role in wound signaling process are also discussed in the chapter.