INTRODUCTION

Choice of law in international arbitration is a topic – one among many – that Arthur von Mehren excelled at. His contributions in this field admirably combine the analytical brilliance of a world-leading conflicts law scholar, the impressive expertise of an equally world-leading comparative lawyer, and insights in concept, structure, and functioning of multilevel judicial proceedings ripened over decades. In addition, Arthur von Mehren could draw on his rich practical experiences as an arbitrator, and it was of particular importance to him to pass on his profound knowledge to the next generations: not only did he copublish one of the leading educational text books on international commercial arbitration, but he also continued to teach his strongly demanded course on international commercial arbitration at the Harvard Law School, which I had the privilege of attending during my time as Story Fellow of 1998/99.

This contribution deals with one particular issue of choice of law in international arbitration: it seeks to identify the source and nature of mandatory elements in the process of law selection, that is, the elements an arbitral tribunal is bound by while determining the applicable law. Evidently, any arbitral tribunal is primarily bound by the parties' will including their choice of law – based on their choice of choice-of-law rules that, in turn, grant party autonomy. However, the parties' freedom to choose choice-of-law rules might not be unlimited.