Flexible solid-state supercapacitors have gained immense interest in the area of energy storage owing to their widespread use in modern smart and wearable electronics. In this chapter, we review the requirements and state-of-the-art advancements in the field of flexible solid-state supercapacitors based on 2D materials. This book chapter begins with the factors and critical elements considered while fabricating flexible supercapacitors, such as cell design (planar, sandwich, cable/fiber), solid/gel electrolytes (aqueous, organic, ionic), and electrode materials. The next sections briefly summarize the latest developments of the 2D materials as flexible electrodes, which can be freestanding, or substrate supported with flexible polymer gel electrolyte. Subsequently, a detailed summary of each 2D material (graphene, transition metal oxides/hydroxides/dichalcogenides, MXenes, and black phosphorus) utilized for flexible supercapacitors has been discussed. The properties of mechanical flexibility and its effects on electrochemical performance have been listed for all 2D flexible electrode materials. The final section highlights the current challenges and future perspective on research on flexible solid-state supercapacitor devices. © 2021 Elsevier Inc. All rights reserved.