Reactive oxygen species (ROS) are highly reactive molecules that play a crucial role in cancer development and progression. Elevated ROS levels are detected in almost all cancers, promoting tumor growth and survival. However, tumor cells also express increased levels of antioxidant proteins to counteract ROS, indicating a delicate balance of intracellular ROS levels. The location and concentration of ROS are critical for their cellular functions. Therapeutic strategies aim to fine-tune intracellular ROS signaling to deprive cells of ROS-induced tumor-promoting events or to prevent early events in tumor development using therapeutic antioxidants. This review discusses the generation, detoxification, and cellular effects of ROS, as well as the major signaling cascades they utilize. It also explores the modulation of ROS in therapeutics, including the use of ROS-increasing agents to induce apoptosis and the use of antioxidants to deplete ROS-induced survival pathways. The review highlights the importance of understanding the specific functions of ROS in cancer, such as their role in cell proliferation, apoptosis, cell motility, and metastasis, and their impact on hypoxia, angiogenesis, and redox regulation in cancer stem cells. Finally, it discusses the potential of ROS and antioxidants in cancer therapy and prevention, emphasizing the need for tailored combination therapies based on tumor type, stage, and ROS levels.Reactive oxygen species (ROS) are highly reactive molecules that play a crucial role in cancer development and progression. Elevated ROS levels are detected in almost all cancers, promoting tumor growth and survival. However, tumor cells also express increased levels of antioxidant proteins to counteract ROS, indicating a delicate balance of intracellular ROS levels. The location and concentration of ROS are critical for their cellular functions. Therapeutic strategies aim to fine-tune intracellular ROS signaling to deprive cells of ROS-induced tumor-promoting events or to prevent early events in tumor development using therapeutic antioxidants. This review discusses the generation, detoxification, and cellular effects of ROS, as well as the major signaling cascades they utilize. It also explores the modulation of ROS in therapeutics, including the use of ROS-increasing agents to induce apoptosis and the use of antioxidants to deplete ROS-induced survival pathways. The review highlights the importance of understanding the specific functions of ROS in cancer, such as their role in cell proliferation, apoptosis, cell motility, and metastasis, and their impact on hypoxia, angiogenesis, and redox regulation in cancer stem cells. Finally, it discusses the potential of ROS and antioxidants in cancer therapy and prevention, emphasizing the need for tailored combination therapies based on tumor type, stage, and ROS levels.