This article reviews recent advancements in flexible solid-state supercapacitors (FSSCs), focusing on substrates, electrolytes, and cell designs. FSSCs are gaining attention due to their potential in wearable and smart electronics. The review begins with an introduction to charge storage mechanisms based on electrode materials' structural properties. It then discusses flexible electrodes, including free-standing and substrate-supported materials, such as textiles, paper, metal foils, and polymer-based substrates. The section on flexible gel electrolytes covers aqueous, organic, ionic liquid, and redox-active gels. The article also reviews novel cell designs, introducing emerging electrode materials like MXenes, metal nitrides, metal-organic frameworks, polyoxometalates, and black phosphorus. Potential applications, such as piezoelectric, photo-, and shape-memory supercapacitors, are discussed. Finally, the review highlights current challenges and future research directions in the field.This article reviews recent advancements in flexible solid-state supercapacitors (FSSCs), focusing on substrates, electrolytes, and cell designs. FSSCs are gaining attention due to their potential in wearable and smart electronics. The review begins with an introduction to charge storage mechanisms based on electrode materials' structural properties. It then discusses flexible electrodes, including free-standing and substrate-supported materials, such as textiles, paper, metal foils, and polymer-based substrates. The section on flexible gel electrolytes covers aqueous, organic, ionic liquid, and redox-active gels. The article also reviews novel cell designs, introducing emerging electrode materials like MXenes, metal nitrides, metal-organic frameworks, polyoxometalates, and black phosphorus. Potential applications, such as piezoelectric, photo-, and shape-memory supercapacitors, are discussed. Finally, the review highlights current challenges and future research directions in the field.