H. L. A. Hart proposed one of the most influential accounts of law, according to which law is a union of primary rules, which guide the behavior of the law’s subjects, and secondary rules, which guide officials in recognizing, changing, and interpreting primary rules. Writing at the end of the 1950s, Hart had serious doubts about whether international law meets the necessary criteria for a legal system. But there are several reasons to reconsider his position. One is that international law (...) has grown significantly since then, but a more important reason is that Hart provided an oversimplified description of the necessary and sufficient conditions for law provided by his account, and therefore of the nature of the international legal order. A proper understanding of Hart’s view gives us a richer and more accurate understanding of the essential features of law, but also a less precise yardstick by which to measure and characterize the various systems of rules, including international law. According to this new yardstick, international law fails to meet the criteria for a Hartian legal system, but for reasons other than those identified by Hart. (shrink)