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.The question then arises whether the next iteration of hydrogels can be designed for long-term applications in an in vivo environment with all its complicating agents and factors, and issues such as biodistribution and immune responses. [27][28][29][30] Hydrogels could be prone to dissociation by high shear forces, or the responsiveness to stimuli could be much less sensitive within the body. [31][32][33][34] In this review, we discuss the design of hydrogels for in vivo applications, including for use clinically and commercially. This is not a comprehensive review of the entire field of translational hydrogels, but concentrates on promising results in animal trials. The reader is referred to several reviews which offer a different perspective and provide more detailed information on injectable hydrogels, regenerative scaffolds, and therapeutic delivery. [2,11,24,[35][36][37][38][39]