 The author would like to thank Jan Baedke, Dominic Berry, Soraya de Chadarevian, Elizabeth Hughes, Staffan Müller-Wille, Ulrich Stegmann, and the reviewers for their suggestions and comments. The entry was written at the University of Kassel under funding by the Deutsche Forschungsgemeinschaft (DFG – German Research Foundation) – project nr. 362545428, and finalized while being visiting postdoctoral fellow in the MPRG “Practices of Validation in the Biomedical Sciences” at the Max Planck Institute for the History of Science, Berlin, and postdoc researcher at the University of Lübeck in the Cluster of Excellence “Precision Medicine in Chronic Inflammation” (EXC 2167), DFG project nr.  390884018.