This edited book is focused on antioxidant compounds and their biosynthesis, up-regulation, mechanism of action for selective bioactivity, targeted role and the advancement of their bioactive potential during plant-microbe interaction and other stress conditions. This book also emphasizes on the role of antioxidants in recruiting beneficial microbes in plant surroundings. Antioxidants have multiple biological roles in plants especially in the signalling pathway. These compounds are secondary metabolites produced besides the primary biosynthetic pathway and are associated with growth and development. Besides they also have special role to play during oxidative stress produced via abiotic stimulants or pathogen attack. This understanding of the biosynthesis, signaling and function of antioxidant compounds in plants during stress condition is helpful in restoring plant ecosystem productivity and improve plant responses to a wide range of stress conditions. This book is a useful compilation for researchers and academicians in botany, plant physiology, plant biochemistry and stress physiology. Also the book serves as reading material for undergraduate and graduate students of environmental sciences, agricultural sciences and other plant science courses.