This review outlines the theoretical background of impedimetric biosensors and presents different types of impedimetric immunosensors along with the instrumental approaches that have been so far proposed in the literature for the evaluation of their performance. The electrode assemblies have been classified in four main categories with respect to the electrode material, the type of the insulating layer and the immobilization platform that have been used for their construction. Additionally, some selected works on recent developments in immunosensors, which are based on polymer degradation phenomena, magnetic nanobeads, etc. as well as strategies for the amplification of the measuring signals, are also presented. (C) 2009 Elsevier Ltd. All rights reserved.