In order to promote harmonisation in a more effective manner in the European patent system, it is argued that this should not solely be done through legislation, but through judicial dialogue and cooperation. Through this means of informal harmonisation, progress can be made case-by-case, rather than waiting for legislation to be agreed upon and entered into force. This is already happening to good effect, as displayed through a number of examples, including the most recent example of Actavis v. Eli Lilly [2017] UKSC 48 in the UK Supreme Court. It is proposed by this article that official lines of communication should be opened among all judiciaries and Boards in the European patent system to improve this practice. Judicial cooperation would also be useful to the Unified Patent Court, if it becomes operational. Opening official lines of communication would be an important step towards a further harmonised European patent system and would increase legal certainty in this area.