This article, published in *Clinical Interventions in Aging*, reviews the role of oxidative stress in aging and age-related diseases. Reactive oxygen and nitrogen species (RONS) are produced by various endogenous and exogenous processes and can cause significant damage to cellular components, leading to functional declines and diseases. The oxidative stress theory of aging suggests that age-related functional losses are due to the accumulation of RONS-induced damages. RONS are involved in several age-related conditions, including cardiovascular diseases (CVDs), chronic obstructive pulmonary disease, chronic kidney disease, neurodegenerative diseases, and cancer. Different biomarkers of oxidative stress have been identified, which can provide insights into treatment efficacy and guide therapeutic interventions. The article discusses the pathophysiology of oxidative stress, including the production and sources of RONS, and the mechanisms by which they cause damage to cellular macromolecules. It also explores the relationship between oxidative stress and aging, highlighting the role of cellular senescence and the senescence-associated secretory phenotype (SASP) in age-related diseases. The article further examines the impact of oxidative stress on specific age-related diseases, such as CVDs, diabetes, chronic obstructive pulmonary disease (COPD), chronic kidney disease (CKD), cognitive impairment, and cancer. Biomarkers of oxidative stress, including RONS-induced modifications, markers of RONS generation, markers of antioxidant defense, and downstream functional markers of RONS-induced damage, are discussed. These biomarkers can provide important information about the efficacy of treatments and guide the selection of effective drugs and dosages. The therapeutic approach section reviews various antioxidants and their potential benefits, including vitamins, coenzyme Q10, selenium, polyphenols, and other natural antioxidants. The article also discusses the role of physical exercise in reducing oxidative stress and preventing chronic diseases. Overall, the article emphasizes the importance of oxidative stress in aging and age-related diseases and highlights the need for further research to evaluate the efficacy of antioxidant therapies.This article, published in *Clinical Interventions in Aging*, reviews the role of oxidative stress in aging and age-related diseases. Reactive oxygen and nitrogen species (RONS) are produced by various endogenous and exogenous processes and can cause significant damage to cellular components, leading to functional declines and diseases. The oxidative stress theory of aging suggests that age-related functional losses are due to the accumulation of RONS-induced damages. RONS are involved in several age-related conditions, including cardiovascular diseases (CVDs), chronic obstructive pulmonary disease, chronic kidney disease, neurodegenerative diseases, and cancer. Different biomarkers of oxidative stress have been identified, which can provide insights into treatment efficacy and guide therapeutic interventions. The article discusses the pathophysiology of oxidative stress, including the production and sources of RONS, and the mechanisms by which they cause damage to cellular macromolecules. It also explores the relationship between oxidative stress and aging, highlighting the role of cellular senescence and the senescence-associated secretory phenotype (SASP) in age-related diseases. The article further examines the impact of oxidative stress on specific age-related diseases, such as CVDs, diabetes, chronic obstructive pulmonary disease (COPD), chronic kidney disease (CKD), cognitive impairment, and cancer. Biomarkers of oxidative stress, including RONS-induced modifications, markers of RONS generation, markers of antioxidant defense, and downstream functional markers of RONS-induced damage, are discussed. These biomarkers can provide important information about the efficacy of treatments and guide the selection of effective drugs and dosages. The therapeutic approach section reviews various antioxidants and their potential benefits, including vitamins, coenzyme Q10, selenium, polyphenols, and other natural antioxidants. The article also discusses the role of physical exercise in reducing oxidative stress and preventing chronic diseases. Overall, the article emphasizes the importance of oxidative stress in aging and age-related diseases and highlights the need for further research to evaluate the efficacy of antioxidant therapies.