Hydrogels have been extensively investigated as biomaterials because of their excellent biocompatibility, and recent developments such as 3D printing and the incorporation of dynamic crosslinks have advanced the field considerably. However, the next step of in vivo translational biomedicine requires an understanding of essential hydrogel properties so that they can be designed to overcome the challenges of the living environment. In this review, the stringent design criteria required for in vivo applications are highlighted and recent advances in the repair of organ tissues (heart, bone, eye, etc.) and the therapeutic delivery of bioactive molecules are described. Commercially available hydrogel systems that can be used for translational biomedicine are also discussed, as is the long and sometimes fraught journey from the laboratory to the clinic.