When assessing the sustainability of a particular technology, a number of environmental, economic, and social indicators need to be taken into account. The aim of this paper is to analyze the underlying rationales for the prioritization of all these indicators i.e. the rationale for an integrated sustainability assessment. For this purpose, different alternative paradigms of sustainability are briefly discussed, with the focus on the concepts of weak and strong sustainability, which define a spectrum of views on the possibility to replace environmental capital with human-made capital. We conclude that there is a sound case for the strong sustainability paradigm and we argue that this conclusion has deep implications for the decision-making processes. Firstly, because it implies that a set of thresholds for a number of environmental indicators would need to be agreed upon. Secondly, because it implies that environmental impacts would no longer be ‘tradable' for socio-economic benefits, when they are expected to go beyond the agreed threshold. We suggest that non-compensatory decision-making tools will need to be considered at some point in the process in order to account for the non-substitutability of critical environmental services. Using the concept of ‘planetary boundaries' proposed by Rockström et al. we discuss how such information could be put into practice in decision-making. We suggest that the concept of planetary boundaries can provide both a preliminary basis for the prioritization of environmental impacts and a preliminary supporting argument for the definition of environmental thresholds that enable the use of non-compensatory decision-making approaches. Further work in this area is urgently required.