The principle of impartiality symbolizes the change in the doctrines of UN peacekeeping operations and also the shift of understanding of international order. The traditional UN PKO had a principle of neutrality. But in the 1990s there were serious failures of peacekeeping operations and there appeared cries for change in PKO doctrines. Secretary-General Kofi Annan intentionally distinguished between neutrality and impartiality in favor of the latter. The Brahimi Report and the Capstone Doctrine crystalized Annan’s initiative in defense of impartiality. The difference between neutrality and impartiality is one major issue in the 21st century. It can be noted that there is a change in understandings of international order behind the emergence of the principle of impartiality as a key doctrine of the shift in contents of UN PKOs. The paper argues that the principle of impartiality ushered in the spread of robust operations. Impartiality explains how UN PKOs accommodate new doctrines like protection of civilians (POC) and frequent use of Chapter VII authorities, since impartiality requires more principled peace operations based upon international normative standards of international humanitarian law and international human rights law. This paper then illustrates how the principle of impartiality is crucial in many recent cases of UN PKOs including UNAMID, MONUSCO, UNMISS, MINUSMA, MINUSCA.