Abstract <p>A novel class of polymers has emerged from recent research, designed to alter their physical and/or chemical properties in response to environmental cues. Known as stimuli-responsive or smart polymers, these materials are engineered to respond to pH, temperature, mechanical force, small molecules, biomolecules, and electric or magnetic fields. Among these stimuli, light is particularly attractive due to its nondestructive nature, remote accessibility, rapid responsiveness, tunable intensity, cost-effectiveness, and external programmability. A deeper understanding of the mechanisms underlying light responsiveness is particularly valuable, as it informs the design strategies of light-responsive hydrogels (LRHs). This article demonstrates these mechanisms while presenting the latest design strategies and recent advances in LRHs, emphaszing their growing relevance in biomedical applications. Despite remarkable progress, the potential of LRHs in sensor technology remains underexplored. This study highlights their promise while stressing the urgent need for further research and development in this emerging field.</p> Graphical abstract <p></p>