Plant and plant products are being used as a source of medicine since long. Natural antioxidants that are present in plants and herbs are responsible for inhibiting or preventing the deleterious consequences of oxidative stress. Many Indian medicinal plants are considered to be potential sources of antioxidant compounds. However, the majority of rich diversity of these medicinal plants is yet to be significantly evaluated for such properties. Considering an increased quest to obtain natural antioxidants with broad-spectrum actions and potential antioxidant activity, this book highlights the various methods to assess antioxidant activity of medicinal plants. It also attempts to evaluate the antioxidant activity of some commonly used indigenous plants using different systems of in-vitro assays to provide scientific evidence about their antioxidant property and explore an antioxidant with promising activity. Our results further support the view that some traditionally used Indian medicinal plants are promising sources of potential antioxidants.