PEG hydrogels are widely used in biomedical applications, including controlled release of biomolecules and scaffolds for regenerative medicine. This review discusses the polymerization mechanisms of PEG-based hydrogels and their importance in regenerative medicine. It also covers design criteria for maintaining biomolecule availability and stability, as well as mechanisms for loading biomolecules into PEG hydrogels. Emerging applications of PEG hydrogels, such as spatiotemporal-controlled delivery, hybrid hydrogels, and PEG hydrogels for controlled stem cell differentiation, are also discussed. PEG hydrogels offer unique properties for cell encapsulation and can be tailored for various applications. Different polymerization mechanisms, such as chain-growth, step-growth, and mixed-mode polymerization, are explored, along with their advantages and challenges. The hydrogel properties, including hydrophilicity and anti-fouling characteristics, are important for regenerative medicine. The controlled release of biomolecules in PEG hydrogels depends on factors such as gel permeability, crosslinking density, and the use of degradable linkers. The stability of biomolecules is crucial for maintaining their bioactivity during hydrogel fabrication and release. Loading and release mechanisms in PEG hydrogels include entrapment, tethering, and multiphase loading. PEG hydrogels are also used for spatiotemporal-controlled delivery, hybrid hydrogels for dynamic sensing and actuation, and controlled stem cell differentiation. The review highlights the potential of PEG hydrogels in regenerative medicine and the importance of designing hydrogels that can effectively deliver therapeutics and control cell fate.PEG hydrogels are widely used in biomedical applications, including controlled release of biomolecules and scaffolds for regenerative medicine. This review discusses the polymerization mechanisms of PEG-based hydrogels and their importance in regenerative medicine. It also covers design criteria for maintaining biomolecule availability and stability, as well as mechanisms for loading biomolecules into PEG hydrogels. Emerging applications of PEG hydrogels, such as spatiotemporal-controlled delivery, hybrid hydrogels, and PEG hydrogels for controlled stem cell differentiation, are also discussed. PEG hydrogels offer unique properties for cell encapsulation and can be tailored for various applications. Different polymerization mechanisms, such as chain-growth, step-growth, and mixed-mode polymerization, are explored, along with their advantages and challenges. The hydrogel properties, including hydrophilicity and anti-fouling characteristics, are important for regenerative medicine. The controlled release of biomolecules in PEG hydrogels depends on factors such as gel permeability, crosslinking density, and the use of degradable linkers. The stability of biomolecules is crucial for maintaining their bioactivity during hydrogel fabrication and release. Loading and release mechanisms in PEG hydrogels include entrapment, tethering, and multiphase loading. PEG hydrogels are also used for spatiotemporal-controlled delivery, hybrid hydrogels for dynamic sensing and actuation, and controlled stem cell differentiation. The review highlights the potential of PEG hydrogels in regenerative medicine and the importance of designing hydrogels that can effectively deliver therapeutics and control cell fate.