This book analyses the principle of equality from three perspectives: public international law, private international law and EU law. It is the first book in English providing a comprehensive overview of this principle in these areas of law and showing the current trends and issues concerning its application. Its main goal is to understand whether and to what extent the principle of equality has been affirmed in public and private international law, as well as EU law, and what - if any - the common core of this principle is.The analysis carried out in this contributed volume starts from general analyses of the principle of equality in the areas of the law covered by the book and then discusses the principle in more specific areas, such as human rights law, international adjudication (including investment law) and the law of international organizations.