One of the defects of International Law is obscurity and uncertainty. Codification not only makes the rules clear and certain but also reconciles conflicting and divergent views. Codification means systematization of or reducing the whole body of rules into code in the form of enacted law. It enhances the efficacy of International Law by increasing its binding force. It will be easier and convenient to amend the codified International Law so as to keep it at pace with the tide of time. The history of codification of International Law dates back to the 18th century when idea for codification was conceived by Jeremy Bentham. Later on, several declarations and conferences held on warfare, neutrality etc. proved to be significant. Much impetus was given to the process of codification under League of Nations. But, such efforts faded away as they were not able to avoid World War II however, they provided incentives to set forth the stage for the codification of International Law. When United Nations was established and UN Charter was adopted, its article 13(1) (a) made it imperative on General Assembly to ‘encourage the progressive development of International Law and its codification’. For this purpose the International Law Commission was established with the same objective at its core. Its task is to undertake survey, draft and recommend the topic for codification. The establishment of ILC proved a turning point in the ‘codification movement’ with number of feats under its head. This article seeks to analyze the role played by the United Nations in the codification of modern International Law and various achievements of International Law Commission established under its aegis.