This book offers a systematic legal analysis of referendums on sovereignty issues and is based on my Ph.D. dissertation from the University of Zurich, Faculty of Law which was approved on 11 December 2013. The concern for authenticity has led me to prefer a facsimile publication except for certain formal modifications of the text. This is the main reason for the exclusion of certain referendums held in 2014, such as the ones in Crimea, Scotland and Catalonia. Putting aside the challenge of updating, these subsequent developments have, fortunately, reconfirmed my belief from the very beginning of this project that the use of referendums is growing in the resolution of sovereignty conflicts in international and national politics. I hope this book will serve as a useful reference for researchers in international and constitutional law who have a scholarly interest in the subject of sovereignty referendums.