The sources of international law are multilateral treaties, bilateral treaties, and customary international law. These agreements are drafted during extensive negotiations at diplomatic state conferences. Upon agreement, these treaties are opened for signature or ratification by states. Once ratified by an agreed number of states, they become binding on member states. Other sources of international law include treaties, customary international law, and general principles of law found in most domestic legal systems. Judicial decisions and scholarly writings also serve as secondary sources of international law.

In the 15th century, a confluence of factors led to the development of international law. Greek scholars from the Byzantine Empire and the printing press helped shape this body of knowledge. Humanism and the concept of individual rights were also fostered. Additionally, increased European exploration prompted scholars to expand the concept of international law beyond the boundaries of European Christian nations. Moreover, the rise of centralized states such as Spain and France necessitated the creation of more sophisticated rules to govern international affairs. These scholars came to consider Hugo Grotius’ De jure belli ac pacis as the foundation of international law.

In contrast, purely empirical analysis presents a difficulty in communicating normative arguments in international law. Collecting data on violations of human rights norms may be informative, but it does not show how these norms affect social life. While they may provide examples of non-compliance, such data are often inaccurate in revealing the range of social effects of certain norms. International law is a complex body of rules that often requires expert interpretation.