Do we really care about unintended outcomes? An analysis of evaluation theory and practice

•Programme, policies and products can produce ‘unintended outcomes’.•We need to study unintended effects for ethical (doing no harm) and technical (using them to improve interventions) reasons.•A critical examination of evaluation theory and practice is undertaken and it is found that:•despite wider acknowledgement of the phenomenon of unintended outcomes, evaluation theory is not adequately developed to examine such effects.•International development evaluation practices failed to focus on such effects despite a general consensus about their importance. The concept of ‘unintended outcomes’ has a long history. Contributions to the topic have appeared under the guise of various disciplinary lenses, including programme evaluation. There is now solid consensus among the international evaluation community regarding the need to consider side effects as a key aspect in any evaluative study. However, this concern often equates to nothing more than false piety. In this article, shortcomings of existing theoretical developments to evaluate unintended outcomes are identified. Current evaluation practices in international development are then analysed to demonstrate ways in which unintended outcomes remain peripheral. Reasons for neglect are discussed and the need for a stronger re-focusing on unintended effects of development interventions is advocated.