This chapter deals with the codification efforts of the International Law Commission (ILC). It analyzes three law of treaties Conventions that were drafted by the ILC. First, it analyzes the most successful of all the Conventions, the 1969 Vienna Convention on the Law of Treaties. It mostly has codified existing norms of customary international law but also introduced, inter alia, a revolutionary regime of reservations to treaties and dealt with a controversial (at the time) notion of the norms of jus cogens. This Convention has acquired an iconic status in international law and has become the most significant tool regulating the relations between states. The 1986 Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations has never entered into force. It has not proven as successful as its predecessor due to certain unresolved questions relating generally to the functions of international organizations. The 1978 Vienna Convention on Succession of States in respect of Treaties has entered into force; however, due to complexities of state succession in general, it has not played a prominent role, regulating mostly succession in respect of treaties of newly independent, post-colonial states. Finally, the chapter also analyzes Draft Articles adopted by the ILC in 2011 on Effects of Armed Conflicts on Treaties. The form to be given to the Articles is under consideration and governments are invited to comment on any future action regarding them. The list of categories of treaties in the annex suggests that due to its subject matter they will continue to operate, in whole or in part, in the event of armed conflict.