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What has been the contribution of surface potential studies during the last four decades to our understanding of insulation physics? Which are the promising techniques emerging in this field? The present review covers the industrial context accounting for the development of surface potential measurements on insulating materials, the way they have been implemented, as well as the great variety of models produced to explain the charging and potential decay mechanisms. Several polarization or transport processes can be responsible for the decay of the potential. Though most of the models initially stemmed from electrostatics and semiconductor physics, around the notion of mobility, experiments on polymers required "thermodynamic" models, describing progressive charge detrapping. We also underline here that the three main different physical processes likely to be involved in the potential decay (dipolar relaxation, dispersive transport, slow detrapping) can lead in disordered materials to the same time response, the challenge being here is to design inventive new procedures to distinguish them. This comment also applies to most of electrical measurements on disordered materials. Kelvin probe microscopy, return voltage and thermostimulated potential measurements also illustrate the multiform development of surface potential measurement techniques, as their future prospects.