Highest national courts in a pluralist legal order are not just responsible for the uniformity and the development of national law, they have become responsible for the application of transnational and European law within the national legal system as well. This changes their position from that of a highest court the top of the pyramid of the national judicial organisation into that of, metaphorically speaking, the spider in a seamless web of (trans)national adjudication. How do they adapt to this changing position? In what sense and to what degree are they responsive to their new tasks and responsibilities? And in what sense are they resistant or ineffective as courts of transnational and European law? How could their functioning as such be improved? Research into these questions necessarily presupposes a comparative and interdisciplinary approach. Comparative, since the highest courts from different (European) legal systems can best be assessed from this perspective (how do they do, relatively speaking?). Interdisciplinary, because this involves research of an institutional, legal, and empirical kind (what kind of institutional, legal and empirical characteristics and circumstances are responsible for the differences in performance?).