On October 18, 2011, the ECJ rendered its decision in the matter C-34/10, the so-called “Brüstle” patent, in which the Bonn, Germany-based stem cell researcher Oliver Brüstle claimed cells which had been isolated from a human embryo. As part of its decision, the ECJ had to interpret the term “embryo”. According to the European Biotechnology Directive, the use of embryos for industrial and/or commercial purposes is excluded from patentability. The ECJ interpreted the term very broadly. In the ECJ’s view, an embryo comes into existence upon fertilization of the human egg cell. This definition left open the question of when the embryonic developmental stage is completed and, thus, when a further stage of differentiation commences which is no longer deemed an embryo in the sense of the excluding provision. All this is quite alarming, especially considering the fact that the ECJ excludes from patentability every invention – and not just stem cell inventions – as long as the technical teaching underlying the patent requires the use of an embryo as starting material, regardless of the stage this embryo is in. This broad and unfortunately incomplete definition of the term “embryo” raises numerous questions with regard to patentable subject matter, not only in the field of stem cell research, but also for example in the field of prenatal diagnostics or pre-implantation diagnostics (PID). In particular, it will now be difficult for researchers working in these fields to determine which work may be open to patent protection, and which work the ECJ decision is intended to exclude. In the wake of the recent decision, there unfortunately still remains a long path to legal certainty in this research sector.