Carbazole Modified Polysiloxanes have been cross-linked to form electrochromic thin films. Composite materials containing a variety of counter-ions have been found to undergo reversible switching between a colourless (reduced) and green (oxidised) state, with the reproducibility being determined by the growth rate and the nature of the counter-ion. Investigations in a two terminal transmitting cell structure reveal the density of dicarbazolyl moieties to be approximately 10(21)cm-3. The rate limiting step in the colouration process appears to be ion, transfer across the electrolyte-film interface, whereas bleaching appears to be controlled by a double extraction mechanism. Films containing different spacer groups possess similar colouration times, while bleaching rates vary significantly.