Abstract : Spanning almost the entire second half of the twentieth century, and concerning the majority of domains of international law, and intensified by numerous borrowings from the history of political thought, philosophy, and sociology, the work of René-Jean Dupuy is at once of a striking density and yet of a remarkable diversity. It doesn't lose, however, its unity, which is grounded in the author's constant willingness to probe the change from the "world of cities" to the "City of the world". Profoundly influenced by the work of Georges Scelle, it's in a structural resolution of the problem raised by the multiplicity of "powers" that René-Jean Dupuy surveys the elements for such an evolution. Nevertheless, having quickly perceived the limits of his works, he turned more decisively towardq "ethics". Thus, Dupuy essentially studies how the different actors of the international legal order regard the international community and humanity. Consequently, he proposes to determine the meanings to organize the plurality of the ethics in the underlying unity of what Dupuy labels englobants, the emergence of which wwas precipitated by the upheavals that occurred during the twentieth century. This shift from "powers" to "ethics" does not form a break in the work of an author who would progressively abandon legal analysis in order to devote himself to works of a sociological or indeed of a philosophical nature. The work of René-Jean Dupuy rests entirely on an equivalence that he borrows from Scelle : law is at the conjunction of ethics and power. Thus, the work of Dupuy firts and foremost questions the jurist and calls him to reflect upon the role of his discipline when confronted by the challenges of the "earth city" under construction, and in so doing, on his place as a member of this city.