It was L. H. Baekeland who, in his 1916 Perkin Medal address to the Society of Chemical Industry in New York, said ‘Commit your blunders on the small scale and make your profits on the large scale’. While he said this in the context of developing industrial chemical processes, its wider significance lies in the obvious but also possibly under-appreciated point, viz. the measure of success (whatever this might be) in any multi-step activity relies on the product of this measure for each individual step and not the sum. Also implicit in Baekeland’s dictum is the importance of appreciating and anticipating scaling issues in technological development. While these are bread and butter matters for engineers, technologists and chemical companies engaged in such development, this is less true for academic chemists and others not directly involved in, or responsible for, the development process. Furthermore, when applied to global questions relating to systems for more sustainable energy, fuel and chemicals production, the issues of scale (and scalability) become even more complex and their wider appreciation yet more critical. In a multi-step chemical synthesis the overall yield will be the product of the yields of the individual steps: a low yield for a single critical (and possibly overlooked) step will impact on the overall yield. In an industrial context, there is a need to decide whether to amend the synthetic route to avoid the low-yielding step; or, to research it in the hope of improving the yield through better understanding. An industrial operation (governed by the primary imperative of providing returns on investment) will usually opt, pragmatically, for the quicker less-costly option after (if following Baekeland’s advice) fully evaluating the pros and cons of the alternatives and applying expert judgement before coming to a decision. A similar dilemma applies to the more complex problems found in the development and assessment of sustainable technologies, where there may be disagreement about the relative merits of research-led or a systemsdesign-led options (and even disagreement as to which the critical problematic step or steps might be). These are so-called ‘wicked’ (as opposed to ‘tame’) problems, multifaceted and multi-stakeholder, characterised by a lack of consensus on the goals to be aimed at, influenced by a range of scientific and other disciplines and subject to the flux of public opinion. With scarce resources and (in terms of the timescales of technological change) little time to identify more sustainable technologies how can we decide which are to be preferred: radical but disruptive technological approaches (such as the hydrogen economy) or seemingly more ‘drop-in’ alternatives (such as hydrocarbon production from biomass)? As it will not be possible to research and develop all the conceivable alternatives, back-of-the-envelope order-of-magnitude assessments are needed to rule out the obvious non-starters. Or, as Murray Gell-Mann said, ‘it is vitally important that we supplement our specialized studies with serious attempts to take a crude look at the whole.’ However, sustainability-related research, development, impact assessment, promotion and comment by interestgroups and media now often proceed in parallel, seeking to influence as well as to inform (and too often it is difficult to distinguish between the two). The resulting confused and confusing environment makes difficult the development of an informed awareness of reliable evidence, a balanced assessment of its significance and the provision of a sound foundation for judgement and decision-making, whether by N. Winterton (&) Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK e-mail: N.Winterton@liverpool.ac.uk