Hydrogels are promising materials for flexible electronics due to their high flexibility, conductivity, and tunable mechanical properties. This review discusses the latest developments in hydrogel-based flexible electronics, including applications in energy storage, touch panels, memristors, and sensors such as temperature, gas, humidity, chemical, strain, and textile sensors. The review also covers synthesis methods and fabrication techniques for hydrogels, as well as challenges and future research directions for flexible and portable electronic devices. Hydrogels are three-dimensional polymer networks that can absorb and retain large amounts of water. They are classified into electron-conductive and ion-conductive types. Electron-conductive hydrogels use materials like metal nanoparticles, carbon-based nanomaterials, and polymers to achieve conductivity. Ion-conductive hydrogels rely on the mobility of water-soluble ions for conductivity. Hybrid conductive hydrogels combine both types for enhanced performance. Techniques to enhance hydrogel performance include modifying conductivity by adding conductive dopants, improving mechanical properties through crosslinking and doping, and enabling self-healing properties. The fabrication of sensors involves methods such as deposition, etching, and printing. These techniques are crucial for developing flexible and wearable sensors that can detect various stimuli, including temperature, chemical, and gas changes. Applications of hydrogels in flexible electronics include touch screens, displays, and sensors. For example, hydrogel-based touch screens can detect touch positions and movements with high sensitivity. Temperature sensors use hydrogels to detect changes in ambient temperature through resistance or fluorescence changes. Chemical and gas sensors utilize hydrogels to detect pH, ammonia, and nitrogen dioxide with high sensitivity and selectivity. The review highlights the potential of hydrogels in various fields, including medical diagnostics, wearable technology, and environmental monitoring. Future research directions include improving the mechanical and electrical properties of hydrogels, enhancing their sensitivity and selectivity, and developing self-powered and self-healing hydrogel-based devices. Overall, hydrogels offer a promising solution for flexible electronics due to their unique properties and versatility in various applications.Hydrogels are promising materials for flexible electronics due to their high flexibility, conductivity, and tunable mechanical properties. This review discusses the latest developments in hydrogel-based flexible electronics, including applications in energy storage, touch panels, memristors, and sensors such as temperature, gas, humidity, chemical, strain, and textile sensors. The review also covers synthesis methods and fabrication techniques for hydrogels, as well as challenges and future research directions for flexible and portable electronic devices. Hydrogels are three-dimensional polymer networks that can absorb and retain large amounts of water. They are classified into electron-conductive and ion-conductive types. Electron-conductive hydrogels use materials like metal nanoparticles, carbon-based nanomaterials, and polymers to achieve conductivity. Ion-conductive hydrogels rely on the mobility of water-soluble ions for conductivity. Hybrid conductive hydrogels combine both types for enhanced performance. Techniques to enhance hydrogel performance include modifying conductivity by adding conductive dopants, improving mechanical properties through crosslinking and doping, and enabling self-healing properties. The fabrication of sensors involves methods such as deposition, etching, and printing. These techniques are crucial for developing flexible and wearable sensors that can detect various stimuli, including temperature, chemical, and gas changes. Applications of hydrogels in flexible electronics include touch screens, displays, and sensors. For example, hydrogel-based touch screens can detect touch positions and movements with high sensitivity. Temperature sensors use hydrogels to detect changes in ambient temperature through resistance or fluorescence changes. Chemical and gas sensors utilize hydrogels to detect pH, ammonia, and nitrogen dioxide with high sensitivity and selectivity. The review highlights the potential of hydrogels in various fields, including medical diagnostics, wearable technology, and environmental monitoring. Future research directions include improving the mechanical and electrical properties of hydrogels, enhancing their sensitivity and selectivity, and developing self-powered and self-healing hydrogel-based devices. Overall, hydrogels offer a promising solution for flexible electronics due to their unique properties and versatility in various applications.