How might one tell the histories of China and India – two countries that have come to be seen as twenty-first-century giants? How might one tell of how they look to the world and to each other? In this issue we juxtapose, connect and compare the two. Ours is an attempt at a historiography of twentieth-century modernity in China and India beyond the encouragement of Euro-American historiography. We seize this opportunity provided by the contemporary engagement and concern with the two countries to reinterpret the narratives of their twentieth-century transformation, which are far from settled at the moment. We bring historical knowledge to speak usefully to the excitement, anxiety and aspiration around science and technology in China and India. We bring the same to speak meaningfully to the cynicism, admonition and expectations that the world has of them. We use China and India as a method of exploring new historiographical questions of science. We are invested in extending the relevance of studying China and India to the world at large through connections, references and juxtaposition, and by raising questions that, on the one hand, expose the limits of the Euro-American experience and, on the other, open up the intellectual and historiographical space for narratives and theoretical frameworks that are not tied to geopolitical significance. This paper sets out these issues and introduces the papers of the collection.