Ten years or so ago the concept of using a number of sensors ( an array) simultaneously and analysing the combined response was postulated. Like many good ideas it had been borrowed from nature and is the principle behind olfaction (hence the popularity of the term ‘electronic nose’ in some quarters). Analysing information from an array of sensors requires intensive data processing. The array concept has come of age with the advent of fast and relatively cheap computers. Array sensor devices contain a number of different individual sensors which respond to stimuli. The extent to which each individual sensor responds will depend upon its affinity for a given analyte. The data provided by each of the sensors is recorded and sophisticated information processing algorithms are used to make inferences about the stimulus made (identity, quality etc.).