The question of what is, and what is not, part of international law is fundamental in shaping its current form and its development. Traditionally, treaties between states and state practice were seen as the primary means with which to create international law. However, the definition of what the sources of international law are, and how they operate, has been questioned in significant ways. Particularly this has been seen in the more recent developments in the notion of customary international law, which stands alongside international treaties and instruments as a key foundation upon which.