Diabetes mellitus (DM) is one of the common metabolic disorders and 2.8% of the population suffers from this disease throughout the world and it may cross 5.4% by the year 2025. Herbal medicines have been the highly esteemed source of medicine throughout human history. Plants are widely used today indicating that plants are a growing part of modern, high-tech medicine. The medicinal plants, besides having natural therapeutic values against various diseases and considerable works have been done on these plants to treat DM, describes that the antidiabetic activity of medicinal plants is due to the presence of alkaloid, phenolic compounds, flavonoids, terpenoids, saponins, xantone and other constituents which show reduction in blood glucose levels. Currently available therapeutic options for non–insulin-dependent DM, such as dietary modification, oral hypoglycemics, and insulin, have limitations of their own. The present book covers active natural compounds isolated from medicinal plants that have shown experimental or clinical antidiabetic activity.