Ischemia-reperfusion (I/R) injury (IRI) is a multifaceted pathophysiological phenomenon that happens when blood flow is restored to a tissue following a duration of ischemia or oxygen deprivation. The reintroduction of oxygen paradoxically leads to further tissue damage and dysfunction, primarily driven by oxidative stress. This chapter delves into the mechanisms of oxidative stress in IRI, highlighting the role of reactive oxygen species (ROS) generated during the reperfusion phase. It examines how ROS production overwhelms the endogenous antioxidant defenses, resulting in lipid peroxidation, protein oxidation, and DNA damage. The chapter also explores the subsequent activation of inflammatory pathways and cell death mechanisms, including apoptosis, necrosis, and autophagy, that exacerbate tissue injury. Additionally, it discusses potential therapeutic strategies aimed at mitigating oxidative stress, such as novel pharmacological agents and nutraceuticals. Through an understanding of oxidative stress and its implications in IRI, this chapter aims to provide insights into the development of targeted interventions to improve clinical outcomes in conditions such as stroke, myocardial infarction, and organ transplantation.