Hydrogels (like the light-responsive dye-labeled gels pictured on the cover) have the potential to advance the fields of medicine and polymer science as useful components for “smart” devices. Notably, stimuli-responsive hydrogels respond to external stimuli – such as mechanical motion, chemical activation, pH changes, and the application of heat or light – by swelling of the three-dimensional network. Often, these materials display large physiochemical transitions to relatively small stimuli, with the additional benefit of being manipulated under aqueous conditions. In the Review on page 1084 of this joint special issue between the Journal of Polymer Science, Part A: Polymer Chemistry and Part B: Polymer Physics, Jason Locklin et al. highlight recent advancements in stimuli-responsive hydrogels. The stimulus, fabrication methods, design constraints, and novel stimuli-responses are discussed.