Keynote Speech on the 50th Anniversary of the Vienna Convention on the Law of Treaties Department of Foreign Affairs 26 November 2019 Justice Antonio T. Carpio (Ret.) Acting Secretary Enrique Manalo, Undersecretary Eduardo Malaya, Atty. Igor Bailen, other officials and employees of the Department of Foreign Affairs, distinguished guests, friends, a pleasant afternoon to everyone. Thank you for inviting me here this afternoon to join you in celebrating the Golden Anniversary of the Vienna Convention on the Law of Treaties. As you know, the most important source of international law are treaties. Treaties regulate relations between and among states. Treaties constitute the law between and among treaty states. Treaties must be observed faithfully between and among treaty states as expressed in the maxim pacta sunt servanda. Harmonious relations between and among treaty states can be maintained only if states uniformly apply and interpret treaties that regulate their relations. Treaties cannot operate to regulate relations and conduct of states if treaty states have different interpretations of treaties to which they are parties. There can be no effective dispute settlement between and among treaty states without uniform and universally accepted rules of treaty interpretation.