This review discusses recent advances in flexible solid-state supercapacitors (FSSCs) for smart and wearable electronics. FSSCs are promising energy storage devices due to their flexibility, safety, and compatibility with wearable applications. The review covers key aspects including charge storage mechanisms, flexible substrates, electrolytes, and novel cell designs. It highlights the importance of flexible electrode materials, such as MXenes, metal nitrides, metal-organic frameworks, and black phosphorus, which offer high energy and power densities. The review also discusses flexible gel electrolytes, including aqueous, organic, ionic liquid, and redox-active gels, which enhance the performance of FSSCs. Recent developments in flexible substrates, such as carbon paper, textiles, and polymer-based materials, are also highlighted. The review emphasizes the need for further research to improve the performance and practical applications of FSSCs, including piezoelectric, photo-, and shape-memory supercapacitors. The review concludes with a discussion on the challenges and future directions in the development of FSSCs for next-generation wearable and implantable electronics.This review discusses recent advances in flexible solid-state supercapacitors (FSSCs) for smart and wearable electronics. FSSCs are promising energy storage devices due to their flexibility, safety, and compatibility with wearable applications. The review covers key aspects including charge storage mechanisms, flexible substrates, electrolytes, and novel cell designs. It highlights the importance of flexible electrode materials, such as MXenes, metal nitrides, metal-organic frameworks, and black phosphorus, which offer high energy and power densities. The review also discusses flexible gel electrolytes, including aqueous, organic, ionic liquid, and redox-active gels, which enhance the performance of FSSCs. Recent developments in flexible substrates, such as carbon paper, textiles, and polymer-based materials, are also highlighted. The review emphasizes the need for further research to improve the performance and practical applications of FSSCs, including piezoelectric, photo-, and shape-memory supercapacitors. The review concludes with a discussion on the challenges and future directions in the development of FSSCs for next-generation wearable and implantable electronics.