This book addresses questions in connection with the international legal regime on demands for secession, which have arisen in various States. More specifically, it examines the unilateral declarations of independence by Kosovo in 2008, and by Crimea and its subsequent annexation by the Russian Federation in 2014. The work investigates the two cases so as to shed light on the international legal regime affecting entities that are smaller than a sovereign State. It analyzes the relevant principles of international law, the intention being to determine their scope and review them in light of the most recent practice and developments in international law. In turn, the book examines and explains the events of relevance for international law that occurred in the changing situations in Kosovo and Crimea. On the basis of these legal considerations, it explores how the international community can respond when faced with situations that may violate international law, together with the effectiveness of various measures. It also discusses whether certain situations might be legitimate as a concept could now be emerging that secession may be justified in specific circumstances, such as serious and widespread violations of basic human rights.