An overview is given of the electrochemical behaviour of aromatic 1,3,4-oxadiazole polymers and oligomers both in solution and in ultra thin films. The rigid poly(p-phenylene-1,3,4-oxadiazole) (p-POD) can easily be n-doped electrochemically and the resulting electronic structure supports a facile charge transport. In contrast, the meta-isomer (m-POD) was electrochemically inactive. Other thermostable fully aromatic poly(l,3,4-oxadiazole)s can also be electrochemically n-doped. In the anodic sweep region all poly(l,3,4-oxadiazole)s are electrochemically inactive or an irreversible oxidation peak appears. Both the electronic properties of the aromatic unit in the polymer backbone and their mesomeric effects have a great influence on the electrochemical redox behaviour. An enhanced conjugation length of the π-electrons lower the reduction potentials and stabilise the radical anions formed in the electrochemical reduction process. Whereas poly(arylene-l,3,4-oxadiazole)s containing oxygen or other non-conjugated groups in the main chain are not electrochemically active, silicon containing poly(l,3,4-oxadiazole)s can be reversibly n-doped. The doping and undoping processes are accompanied by reversible colour changes of the POD films. In-situ u.v.-vis spectroscopic data give evidences for the formation of electronic states like polarons and bipolarons.