This book introduces a novel approach to comprehending and assessing oxidative stress and antioxidant activity as fundamental components in both health and disease. It explores the advantages and peculiarities of innovative electrochemical methods for estimating and monitoring these processes. Recognizing the electrochemical nature of oxidative stress, the book advocates for electrochemical methods as the preferred means of determination. A central focus of the book is the presentation of a new electrochemical method for evaluating oxidative stress and antioxidant activity: potentiometric determination. The book presents results of antioxidant activity analyses for both healthy individuals and patients with diverse pathologies. Additionally, the book discusses the prospective advantages of employing potentiometry as a monitoring tool in areas such as diet, sports, and wellness. Further considerations extend to the future applications of oxidative stress monitoring, encompassing wearable devices, sensors, non-invasive assessments, and telemedicine. In short, this book establishes the method's credibility as a diagnostic criterion for studying oxidative stress across laboratory settings, bedside applications, and everyday life.