Stretchable supercapacitors can function in versatile environments under multiple mechanical deformations including stretching, bending, twisting and compression, which has implications for powering wearable electronics and implantable biomedical devices, where adaptability and compliant mechanics are required. This review covers the recent advances in the field of stretchable supercapacitors with the focus on materials and their design principles. Firstly, we discuss material aspects on stretchable supercapacitor electrode composition, which includes carbon-based materials, metal-based materials, and conductive polymers. Then, we describe novel strategies to construct 1D, 2D and 3D supercapacitors, highlighting their stretchability and electrochemical performances. Furthermore, we cover extra add-on functionalities that made stretchable supercapacitors ultrathin, transparent or self-healable, as well as their integration with other energy conversion devices. Finally, we discuss the challenges and opportunities in the future developments and optimization of stretchable supercapacitors.