This chapter discusses the necessity to develop flexible energy storage devices. The main efforts are first paid to describe the history and recent advancements in flexible supercapacitors/batteries. Special attention is paid to carbon-based materials for supercapacitors, conductive carbon cloth-, paper-, and insulating textile-based electrodes for batteries, etc. Some recent applications of flexible supercapacitors/batteries are further described. To satisfy the requirements of high-performance flexible electronics, considerable efforts have been devoted to seeking compatible power systems such as flexible supercapacitors and lithium-ion batteries. Nowadays, conducting polymers applied for flexible supercapacitors mainly include polyaniline, polypyrrole, polythiophene, and their derivatives. Commonly, the wire-shaped supercapacitors can be classified into parallel, twisted, and coaxial structures. Technically, it is still a challenge to fabricate the coaxial wire-shaped supercapacitors on a large scale.