International Law is primarily made up of statutory instruments and practice.
A great introductory guide on international law and its sources is contained in the following GlobaLex Guide which gives a good overview of the different bodies at play in international law as well as the different sources.
International Law Bodies
Treaties Collections
Historical Treaties (1600-onwards)
Case Law
International Court of Justice
The Court System of the European Union
European Court of Human Rights
The Inter-American Court of Human Rights
International Criminal Tribunal for Rwanda