PurposeThis conceptual paper aims to examine theoretical issues in the proactive ethical assessment of technology development, with a focus on uncertainty. Although uncertainty is a fundamental feature of complex technologies, its importance has not yet been fully recognized within the field of ethics. Hence, the purpose of this paper is to study uncertainty in technology development and its consequences for ethics.Design/methodology/approachGoing on the insight of various scientific disciplines, the concept of uncertainty will be scrutinised and a typology of uncertainty is (...) proposed and introduced to ethical theory. The method used is theoretical and conceptual analysis.FindingsThe analysis results in questions with regard to the collection of information about the object of assessment and the framework of assessment. Moreover, based on the insights of the analysis of uncertainty, it is argued that substantive ethical theories prove to be inapt for the ethical assessment of complex technology development and therefore require a concomitant procedural approach. The paper concludes with requirements for any future ethics of technology under uncertainty.Originality/valueThe value of the paper consists in establishing the need of researching and incorporating uncertainty in ethics. The results are consequently of practical and theoretical interest for anyone working in the field of ethics and technology. (shrink)