The Casimir Research School (Casimir), established in 2004 by the Kavli Institute of Nanoscience at Delft and the Leiden Institute of Physics (LION), aims for an improved education of young researchers towards a PhD degree. A major attraction of academic institutions is the interplay between young creative and ambitious students with experienced researchers and educators. It leads to a variety of hopefully ground-breaking new research results and to highly educated people who will find their way in various jobs in industry, institutions and academia. Hence, PhD students need to focus but should not become narrow-minded and should also be skilled communicators and project-planners. Leiden and Delft have decided to take on this demanding task jointly, which creates the opportunity for students to be exposed to a larger variety of research-fields and international experts, as well as to organize jointly advanced courses and workshops. About 190 PhD-candidates, 83 post-docs and 85 senior researchers participate.