Antioxidants are vital compounds that protect cellular components by neutralizing free radicals and mitigating oxidative stress, which can lead to molecular damage and disease progression. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play dual roles in biological processes, acting as signalling molecules at moderate levels but causing damage when overproduced. Antioxidants, derived from endogenous or exogenous sources, maintain redox homeostasis through enzymatic systems and small-molecule scavengers like vitamins and phytochemicals. Antioxidants have been used for preservation and ageing mitigation, with modern applications extending to food, cosmetics, and therapeutic strategies for different chronic and acute diseases. Antioxidants can be categorised according to their characteristics, mode of action, and source. They function as direct radical scavengers, metal chelators, and enzyme modulators, emphasizing their critical role in cellular defense. Understanding their mechanisms and optimizing their therapeutic and dietary applications could significantly enhance health outcomes and advance antioxidant utilization across industries.