In this special issue of History of Political Economy, economic historians and historians of science and engineering discuss how economics and engineering came together in the twentieth century. Many economists and historians in the field have argued that, in recent years, economics has become closer to engineering than to science; however, few have attempted to study the historical contingencies through which such an alleged process took place, its involvement in the economics discipline, and its wider role in society. The contributors examine the interactions between economists and engineers as they collaborate or compete to solve complex socio-technical problems, such as warfare, the design and improvement of communication systems, and the pricing of electricity. The authors discuss three aspects of these interactions: their development in specific institutional frameworks, their anchoring in specific national cultures, and the way in which knowledge and practices are transmitted from one field to another.