The degree to which applied technological developments, in the form of patented inventions, are linked to basic science is difficult to determine. However, most patent applications include a list of references – citations – to earlier patents and to non-patent literature (NPL), e.g. scientific papers, that set the boundaries of patents’ claims for novelty, inventive activity and industrial applicability. References are added by the applicant or the patent examiner to reflect the “prior art” that inventions have built upon. Backward citations to NPL can show how close a patented invention is to scientific knowledge, whereas forward patent citations can show the importance of a patent for the development of other technologies.