We present the Manifesto on the Datafication of Mobility Across Borders. Datafication is expanding the potential to produce and circulate information about people at unprecedented speed and scope. This is particularly revealed when people are “on the move” through territories of which they are not citizens. In this Manifesto, we are interested in the datafication practices and infrastructures that produce people as radical others. Practices of datafication and data infrastructures make people on the move knowable, but they do not represent them neutrally. They often enact them as “alterity,” as inherently alien others against whom an “us” can be identified. Allegedly implemented for security purposes, not always well designed, often sloppily applied, practices and infrastructures of datafication of people on the move as others run the risk of subjecting vulnerable people to a perpetual state of precarity and securitization, and polities to long-term policies of expulsion. As sociologists of technology, ethnographers, political scholars, and software developers, we have witnessed with growing concern the recurrent instrumentalization of datafication for assessing identities of people on the move. The ten principles of this Manifesto are drawn from research conducted over seven years by the Processing Citizenship research team and discussed with the international scientific community involved in social studies of science and technology, migration, border and mobility studies, and security studies. We offer these principles based on best practices and empirical observation so that policymakers can hold to account national and European agencies tasked with home security functions, and IT developers can hold to account the infrastructures they design and implement.