Knowledge matters, and states have a stake in managing its movement to protect a variety of local and national interests. The view that knowledge circulates by itself in a flat world, unimpeded by national boundaries, is a myth. The transnational movement of knowledge is a social accomplishment, requiring negotiation, accommodation, and adaptation to the specificities of local contexts. This volume of essays by historians of science and technology breaks the national framework in which histories are often written. Instead, How Knowledge Moves takes knowledge as its central object, with the goal of unraveling the relationships among people, ideas, and things that arise when they cross national borders. This specialized knowledge is located at multiple sites and moves across borders via a dazzling array of channels, embedded in heads and hands, in artifacts, and in texts. In the United States, it shapes policies for visas, export controls, and nuclear weapons proliferation; in Algeria, it enhances the production of oranges by colonial settlers; in Vietnam, it facilitates the exploitation of a river delta. In India it transforms modes of agricultural production. It implants American values in Latin America. By concentrating on the conditions that allow for knowledge movement, these essays explore travel and exchange in face-to-face encounters and show how border-crossings mobilize extensive bureaucratic technologies.