Oxidative stress is a key driver of carcinogenesis, and antioxidants play a critical role in maintaining redox homeostasis and preserving cellular integrity. While antioxidants hold promise as chemopreventive agents and adjunctive therapies in cancer treatment, their dualistic nature complicates their use in clinical practice. Personalised approaches are needed to optimise the efficacy and safety of antioxidant-based interventions, taking into account such factors as the tumour type, stage, genetic background, and redox environment. In this chapter, we aim to elucidate the importance of selected antioxidants in carcinogenesis and cancer therapy by synthesising evidence from epidemiological studies, preclinical research, and clinical trials. By delineating the multiple roles of antioxidants in modulating key pathways involved in cancer development and treatment response, we aim to provide insights into the rational use of personalised antioxidant-based interventions aimed at reducing cancer incidence and improving therapeutic outcomes. Preclinical research has elucidated the molecular mechanisms by which antioxidants modulate key pathways involved in carcinogenesis, including DNA damage repair, inflammation, angiogenesis, and metastasis. In addition, clinical trials have investigated the efficacy of antioxidant supplementation in cancer prevention and therapy, with mixed results depending on such factors as the antioxidant type, dosage, timing, and patient population. Controversies remain regarding the optimal use of antioxidants in cancer therapy, as high doses may potentially interfere with the cytotoxic effects of anti-cancer treatments and promote tumour growth in certain contexts. In addition, emerging antioxidant compounds with potential anti-cancer properties are being actively investigated as novel therapeutic agents. This chapter provides an overview of the importance of selected antioxidants in carcinogenesis and cancer therapy. Oxidative stress is a key driver of carcinogenesis, and antioxidants play a critical role in maintaining redox homeostasis and preserving cellular integrity. While antioxidants hold promise as chemopreventive agents and adjunctive therapies in cancer treatment, their dualistic nature complicates their use in clinical practice.