In the past, evaluation techniques were considered to be “decisional techniques”, “decisional tools”. There was a rough idea that, after the important data had been collected, the technique in question would, by itself, indicate the best decision. Evaluations of this kind clearly depended on the more or less implicit adoption of a “rational-comprehensive model”, which tended to downplay the ethical and political dimension of decisions, while stressing the role of both technique and technicians. This approach has been widely criticized. Partly as a result of such criticism, many evaluation techniques are now considered to be not “decisional tools” but forms of “decision aid”. The problem is that the expression “decision aid” lacks clarity and is by no means unequivocal in urban decisional situations. We believe in this regard that there is a gap in research and in the academic literature. Starting from this conviction, the article presents an investigation of what being a “decision aid” might mean for a technical evaluation today. The aim is to provide a conceptual framework within which to critically revisit and rediscuss the question, with particular regard to urban sustainability issues.