I am delighted to welcome this wonderful contribution to our new series, Elements of International Law: Jus Cogens by Professor Dinah Shelton. When the Elements’ Editors set out to find the best- qualified author to write our jus cogens volume, it was really not a difficult task of discovery. One scholar stood out: Dinah Shelton. Through a remarkable and distinguished career, Professor Shelton has secured her place as one of the most respected authorities in International Law, and her work on the important and complex role of fundamental norms in our discipline is unique and without modern parallel. All of the editors of Elements are honored to have Professor Shelton joining our series. Let me briefly put Professor Shelton’s book into the larger context of Elements of International Law. Some years ago I brought the concept of the series to John Louth and Merel Alsteen, international law editors at Oxford University Press. Together, along with co- editors Douglas Guilfoyle, Stephan Schill, Bruno Simma, and Kimberley Trapp, we structured Elements, chose topics, sought out the best person for each book, and edited their contributions. There are several dozen authors already working on Elements books and we anticipate about six published works in 2020, and ten or so more in each of the next years, in time numbering more than one hundred volumes