1. Aust A (1986) The Theory and Practice of Informal International Agreements International and Comparative Law Quarterly 35:787–812.
2. Evans M (ed) (2018) International Law, 5th edn. Oxford University Press, Oxford.
3. Horbach N, Lefeber R, Ribbelink O (eds) (2007) Handboek Internationaal Recht. T.M.C. Asser Press, The Hague.
4. Jennings Sir R (1981) What is International Law, and How Can We Tell It When We See It? Schweizerisches Jahrbuch für Internationales Recht 37:59–88.
5. Klabbers J (2000) Accepting the Unacceptable? A New Nordic Approach to Reservations to Multilateral Treaties. Nordic Journal of International Law 69:179–193.