This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores the principal statements of the democratic theories of secession since the respect for democratic principles is necessary for the international community to accommodate the secessionist process. It analyzes the normative weight of positions both defending and opposing secession, in a sort of dialogue engaged in an ideal discourse situation. The book looks at the populist use of the secessionist arguments in divided societies and aims to explore the relationship between constitutional democracy and referendum in contexts characterized by new waves of populism. It also looks at the legacy of the seminal Reference Re Secession of Quebec of the Canadian Supreme Court, in order to show the anti-populist potential of that decision which employed a substantive and complex notion of democracy. The book deals with the Crimean issue between Ukraine and Russia and, in particular, on the contradictory elements it entails.