This chapter provides an overview of the third period in the modern history of international commercial arbitration. This period, which started in the 1950s, is the Age of Autonomy. It has been marked by at least three types of autonomy. The first is the autonomy of the mercatocracy, a distinct class of professionals who, having devoted an increasing amount of time and attention to international commercial arbitration, see themselves as experts in international arbitration. A second (and related) type of autonomy is that of the field as a whole. Lawyers, scholars, and professors who had hitherto considered international arbitration as a subcategory of civil procedure or international law started viewing the discipline as a full-fledged field of practice and research. The third kind of autonomy is that of the law expounded by these experts and academics through such concepts as lex mercatoria and the arbitral legal order, which can be seen as attempts to give arbitration a theoretical foundation and explain its development as a system of law in its own right.

In the late 1950s and early 1960s, the idea that a system of international commercial law was gradually replacing domestic laws in the sphere of international transactions began to interest a group of European scholars. Using a bygone expression, they called this phenomenon lex mercatoria, or “law merchant.” The exploration of lex mercatoria also coincided with the emergence of a full-fledged school of thought – what could be described as the French school of international arbitration. As this chapter shows, this was a time of intense renewal, which carried great appeal and led to bold, cutting-edge research. At the same time, vacillating between renewal and anxiety, many scholars strongly disagreed with the existence of lex mercatoria and voiced their disagreement. The first section of this chapter sketches the intellectual history of lex mercatoria; the second investigates its relationship with a nascent school of thought in international arbitration; and the third looks at the quarrels over lex mercatoria that marked the movement from renewal to anxiety.