This chapter gives an account of Pufendorf’s discussion and use of the law of nations. It first outlines his distinctive contribution to contemporary discussions of the topic, namely his rejection rejection, against Grotius, of a specific “positive” law of nations distinct from the law of nature. Secondly it explains how this position relied on Pufendorf’s voluntarist conception of law as the command of a superior and on his conception of the state of nature as devoid of such superiors. The law of nations was simply the law of nature applied to states as composite persons in the state of nature, and the treaties and alliances concluded between them could not amount to a separate and obligatory law of nations. Thirdly, against this background, the chapter shows how Pufendorf discussed the law of war, disentangling the perfect and imperfect obligations of the law of nations from custom, civil laws, and pacts and agreements. Finally, the chapter analyses Pufendorf’s own casuistic use of the law of nations in the various polemical works he published in the service of his sovereigns, especially the King of Sweden, often in line with the theoretical position he developed but also departing from it when opportune.