This book offers a systematic review of the cutting-edge knowledge in stress medicine. Cellular redox imbalance, resulting from overproduction of reactive oxide species (ROS), leads to oxidative stress and subsequent occurrence and development of many diseases, such as cancer, diabetes, pain, etc. In addition, ROS can induce post-translational modification of proteins and play roles through redox signaling pathways. In this book, the authors attempt to re-define the key concepts in oxidative stress, such as oxidative eustress and oxidative distress, revisit the pivotal signaling of oxidative stress in human diseases, and discuss the debate in current anti-oxidant strategies, such as natural products and drug repurposing. This book serves as a reference to graduate students and researchers in this growing field.