Electrospun nanofibres have been confirmed to be very good candidates for ultra-sensitive gas sensors since they greatly improve surface area to volume ratios of coatings, which in turn affect two additional and crucial features for sensors: high sensitivity and fast response time. Electrospinning is a simple method for the deposition of long (up to several centimetres) nanofibres, aligned or non-woven, directly onto suitable transducers. Such a structured layer may have better properties than a compact film, providing faster adsorption and minimising some bulk effects (i.e. long diffusion-desorption time, analyte entrapment, etc.). Electrospun conductive polymers (CPs) have been specifically investigated for developing smart sensors whose electrical properties change upon interactions with the analytes. Polyaniline is one of the most interesting CPs for gas sensing, because of its conductive features, when doped, as well as its thermal stability and sensing performance. The sensing mechanisms are different, depending on the nature of both PANi and the targeting analytes. Thus, various blends of polyaniline and insulating host polymers have been planned, prepared, deposited and studied to optimise the properties of sensors consequent to the combination of the electrical conductivity of CP and of the physical properties of the host polymer. Host polymer carriers cause great modifications to the topology of the interacting surface (diameter and length of the fibres, roughness, porosity, presence of beads and grains, non-woven framework and branched junctions, adhesion, etc.), in addition to the different affinity to the analytes tested. However, they enable electrodes to function over a wider dynamic range of gas or vapour concentrations. The polymer features have been also characterised over a range of water vapour concentrations and temperatures. (C) 2011 Elsevier B.V. All rights reserved.