This book is an introduction to carbon nanotube synthesis and properties; working principles of supercapacitor and lithium-ion battery; as well as the applications of carbon nanotube film in various electrochemical energy storage devices. In Chapter 2, a simple method to fabricate tandem structure of porous silicon film on carbon nanotube film to significantly improve cycling stability of silicon film as lithium-ion battery anode material was demonstrated. With the new structure, both reversible specific capacity and cycling stability are remarkably improved. Carbon nanotube films also exhibit a promising application in stretchable supercapacitors based on buckled carbon nanotube film electrodes for unusual power source applications in Chapter 3. The stretchability depends on the level of pre-stain applied on the PDMS substrate, which could be as high as 30%. This stretchable supercapacitor just enlightens a broad area of stretchable energy storage devices, which are naturally compatible with the developed stretchable electronics.