The CRISPR-Cas9 system is a breakthrough genetic modification technology that allows for deletions, replacements, or insertions in the genome sequence at the target site. The inventors of the CRISPR-Cas9 system and method, the French microbiologist Emmanuelle Charpentier and the American biochemist Jennifer Doudna, were awarded the Nobel Prize in chemistry for this invention in 2020. The so-called CRISPR-Cas9 genome-editing technology enables to edit and/or cleave a DNA sequence in a simple and efficient manner. The CRISPR-Cas9 system includes Cas9 (cleavage enzymes) and guide RNAs (namely, crRNA and tracrRNA) that guide Cas9 to a target site. For this reason, this very important technology has led to a large number of patent applications all over the world. These patent applications and their handling by courts and patent offices attract for this reason much attention in the industries and organisations concerned. In Japan, the Intellectual Property High Court (‘the IPHC’) handed down two important decisions on CRISPR-Cas9 genome-editing related patent applications on 25 February 2020. In the course of the examination proceedings before the Japanese Patent Office (‘the JPO’) both patent applications had been rejected by the Examining Division at first instance and then by the Appeal Board. In both cases, the patent applications were rejected because of lack of novelty over an older patent application which had, however, been published only after the priority date of the subject patent applications (Reason 1, Lack of Novelty, pursuant to Article 29-2 of the Japanese Patent Act) and because of lack of inventive step over a pre-published scientific paper (Reason 2, Lack of Inventive Step, pursuant to Article 29 (2) of the Japanese Patent Act). Against the JPO decisions, appeals were raised before the IPHC. The IPHC on 25 February 2020 rescinded one of the decisions and upheld the other JPO decision. Both decisions of the IPHC of 25 February 2020 will be reported and discussed in this article. The different interpretation of Article 29-2 of the Japanese Patent Act by the IPHC as compared to the JPO was the reason for granting one appeal. In the decisions, the IPHC offers its interpretation of “invention described in the written description of prior application” set out in Article 29-2.