Composite thin films of poly(3,4-ethylenedioxythiophene) (PEDOT)-enwrapped functionalized multiwalled carbon nanotubes (MWCNTs) have been synthesized over multiple length scales by electropolymerization of the monomer without the use of any other supporting electrolyte. The functionalized MWCNTs are incorporated into the positively charged polymer deposit as counterions during oxidative electropolymerization. The morphology, electrochemistry, and electrochromism of the PEDOT-MWCNT films have been compared with those of control PEDOT films doped by triflate ions. Such a comparison enabled us to demonstrate the profound effect of MWCNTs as counterions, realized in terms of better electropolymerization rate, higher conductivity, faster color-bleach kinetics, higher charge storage capacity, and substantially amplified coloration efficiency (η=414 cm2 C-1,*lambda;max = 575 nm, E = -1.5 V) in comparison to the values of η reported to date for PEDOT. The strong interaction between the polymer and MWCNTs, the interconnected nanotubular structures, and the porous framework of the film allow facile charge transport and larger ion uptake during redox switching. Electrochemical investigations on devices based on PEDOT-MWCNT and control PEDOT films established the practical utility of PEDOT-MWCNT films as they show lower charge-transfer resistance, higher diffusional capacitance, and a much smaller amplitude of impedance as compared to control PEDOT films. © 2009 American Chemical Society.