The 2021 Nobel Prize in Economic Sciences has been awarded to David Card of the University of California, Berkeley, “for his empirical contributions to labour economics”, and to Joshua Angrist of MIT and Guido Imbens of Stanford University “for their methodological contributions to the analysis of causal relationships”. This column explains how the use of natural experiments in empirical economics has ushered in much progress in the analysis of causal relationships. The ensuing ‘credibility revolution’ over the past three decades has been transformational for the study of key policy challenges, including education, immigration and the minimum wage.