Much emphasis has been placed on the role that individualism, self-interest and reciprocity have in the formation and function of international legal rules. Rarely has attention been given to the presence of altruism in legal systems, let alone the international legal system. However, this thesis explores and analyses an emerging trend in the creation of diagonal legal relationships between states and people in other countries that is apparent in international law. These legal relationships defy characterisation as individualistic and pose an analytical problem for statist and realist theories. Rather, they are more accurately characterised as altruistic and fit better with the tenets of cosmopolitan theory. Further, the impulse for the emergence of these relationships is a cosmopolitan ideology, which co-exists with a persisting statist ideology, among the major actors in the law-making processes. This results in an observable dialectic between individualistic and altruistic norms in the edifice of international law. Finally, a consideration of the substance of altruism in international law reveals that altruistically oriented legal norms possess certain common characteristics. While individualistic legal norms are more often manifested as strict rules, altruistic legal norms find expression in flexible standards. This suggests that there is a connection between substance and form in international law.