This book provides a comprehensive overview of the oxidative stress related mechanisms in biological systems and the involvement of reactive oxygen and nitrogen species (ROS and RNS), the damage of DNA, proteins, and lipids caused by oxidative stress, the protection of cells and tissues against free radicals, the relation of the oxidative stress to aging and human diseases including cancer and neurological disorders, and the development of new therapeutic approaches to modulate oxidative stress. The current state-of-the-art methodologies including the development of sensors and biosensors for the detection of ROS/RNS and of biomarkers of oxidative stress are also discussed. The book is organized in three overlapping parts, starting with general considerations of the oxidative stress, homeostasis pathways, and ROS mechanisms, followed by chapters discussing the involvement of ROS in particular diseases and concluding with analytical aspects of oxidative stress monitoring. The book provides a solid background on oxidative stress and ROS/RNS generation for novice learners while also offering scientists and practitioners already involved in this field a wealth of information covering the most recent developments in the study of oxidative stress, the role of radical species, novel antioxidant therapies, and methods for assessing free radicals and oxidative stress.