Against the background of European Court of Justice's ruling in the Brustle case, this book deals with the patent eligibility of human embryonic stem cells. Besides a detailed analysis of the relevant legal provisions, it focuses on the interplay of prohibitions of exploitation under public law and prohibitions of patenting. It comes to the conclusion that there is an obligatory connection between prohibitions under public law and prohibitions of patenting. Therefore, it is not permitted to establish assessment criteria for the patented technology beyond the standards of the public law, as exercised by the European Patent Office, the Biotechnology Directive and the ECJ. As a solution, prohibitions of patenting are to be construed as in compliance with the provisions of the public law. With respect to the patent eligibility of embryonic stem cells, the book leads to differentiating results.