AbstractPesticide resistance in arthropods has been shown to evolve by two main mechanisms, the enhanced production of metabolic enzymes, which bind to and/or detoxify the pesticide, and mutation of the target protein, which makes it less sensitive to the pesticide. One route that leads to enhanced metabolism is the duplication or amplification of the structural gene(s) encoding the detoxifying enzyme, and this has now been described for the three main families (esterases, glutathione S‐transferases and cytochrome P450 monooxygenases) implicated in resistance. More recently, a direct or indirect role for gene duplication or amplification has been described for target‐site resistance in several arthropod species. This mini‐review summarises the involvement of gene duplication/amplification in the insecticide/acaricide resistance of insect and mite pests and highlights recent developments in this area in relation to P450‐mediated and target‐site resistance. Copyright © 2011 Society of Chemical Industry