Hydrogels are crosslinked hydrophilic polymers that undergo swelling in water. The gel volume is affected by many environmental parameters including temperature, pH, ionic strength, and solvent composition. Therefore, these factors have been traditionally used for making smart hydrogels. DNA, on the other hand, is a special block copolymer. Incorporation of DNA within a hydrogel network can have several important effects. For example, DNA can serve as a reversible crosslinker modulating the mechanical and rheological properties of a hydrogel. Second, DNA can selectively bind to a variety of different molecules. Attaching these binding DNAs (aptamers) to hydrogel makes it possible to expand the range of stimuli to chemical and biological molecules. At the same time, the gel matrix can also improve DNA-based sensors and materials. For example, the hydrogel can be dried for storage and rehydrated prior to use and the immobilized DNAs are protected from nuclease cleavage. The gel backbone property can also be tuned to affect the interaction between DNA and other molecules. The rational functionalization of DNA in hydrogels has generated a diverse range of smart materials and biosensors. In the last 15 years, the field has made tremendous progress and some of the recent developments are summarized in this review. Challenges and possible future directions are also discussed.