The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT), in different electrolyte-solvent media was studied with cyclic voltammetry, in situ UV-VIS-spectroelectrochemistry. electrochemical quartz crystal microbalance technique (EQCM) and with in situ Fourier transform infrared (FTIR) spectroscopy using external and internal reflection techniques. The effect of polymerization current density and monomer concentration on the formation of the film structure was studied, The redox reactions and the stability of charged films of different thickness were studied with cyclic voltammetry and open circuit potentiometric measurements. FTIR spectra were recorded in situ during step-wise and continuous potential cycling of the polymer films in different electrolytes. A characterization of the doping induced IR-bands has been made.