This chapter looks at the interdependence between the role of courts, the flexibility of constitutions and the rank of international law relative to constitutional law. It claims that the larger the ‘friction surface’ between treaties and constitutional law, the more courts tend to be activist and to assign a higher rank to international law. This friction surface is determined by how often a constitution is amended and by the extent to which the possibilities of constitutional review for apex courts are restricted. This is substantiated by a comparison of the jurisprudence of the highest courts of Germany, Austria and Switzerland. I demonstrate how the Constitutional Court of Germany, due to the comparatively static character of the Grundgesetz, is able to maintain that the Grundgesetz ranks higher than international treaties. The Swiss Federal Court, by contrast, not authorised to assess the constitutionality of treaties and called to interpret a constitution that is amended often, had to choose activism as defence. The case of Austria further substantiates that it is the amendability of the constitution and the extent of constitutional review rather than specific legal traditions that shape the relationship between constitutional and international law.