The EU principle of proportionality as a limit to injunctions in patent law - an analysis of German court practice after the Second Act to Simplify and Modernize Patent Law of 2021

German law has long been known for one of the strongest frameworks for injunctive relief worldwide. In view of this tradition, the 2021 introduction of a proportionality defence in Section 139(1) Sentence 3 of the German Patent Act (Patentgesetz) garnered significant attention in the legal community. Although the new provision has been discussed at length, Section 139(1) Sentence 3 PatG has not yet gained practical significance in case law.This article argues that the proportionality defence must be interpreted and applied in conformity with EU law. From the perspective of EU law, the proportionality requirement is a general and mandatory limitation for all remedies under Directive 2004/48, including injunctive relief in patent law. Member States and their courts may not derogate from the proportionality requirement, not even in favour of the right holder.It is doubtful whether the restrictive application of the principle of proportionality by German courts in patent law injunction cases is compatible with EU law. These doubts concern the balancing of several conceivable aspects of disproportionality and the requirement of an overall assessment of all circumstances in the reasoning of the courts. The doubts also concern the presumed priority of the FRAND defence over Section 139(1) Sentence 3 of the German Patent Act with respect to complex products. The assessment of individual aspects of the proportionality requirement by the German courts is also not free from doubt. This relates to spill-over effects of injunctions if patent protection concerns only a subordinate part of a larger product. Moreover, the criteria of the abuse of rights threshold for non-practicing right holders and the significance of subjective elements in the proportionality test are uncertain.In view of the uncertainties regarding the impact of the EU principle of proportionality, national courts should refer the points mentioned to the Court of Justice of the European Union (CJEU) where they are relevant for the outcome of the case. Due to the high requirements for a finding of an acte clair, a court of last instance is obliged to refer these points to the CJEU.