On 4 December 2009, the European Council unanimously adopted conclusions on an enhanced patent system in Europe, which inter alia intends to establish a new EU patent as well as a new common patent judiciary - the European and European Union Patent Court (EEUPC). The EEUPC will constitute a new sui generis, transnational court system with exclusive jurisdiction in respect of civil litigation related to the infringement and validity of European patents and EU patent. This paper considers this proposal for the establishment of the EEUPC under two basic observations, namely that substantive law requires legal institutions, which support the purposes and policies underlying the substantive law in question, and that legal institutions affect the law. The first observation leads to a discussion of the requirements which a common judiciary in the European patent system should satisfy and different models for the institutional design of such a judiciary. The second observation leads to a discussion of how the EEUPC may affect the European patent system. It is concluded that the need for a common judiciary in the European patent system may be satisfied in different ways and that the EEUPC may not be the optimum solution.