The Åland Strait is a particularly important sea route connecting the Gulf of Bothnia with the Baltic Sea between Sweden and the Åland Islands. The Åland Strait is closely connected to the Åland Islands, which were demilitarised in the international legal treaty ending the Crimean War in the 1850s. Following World War I, the Åland Strait was also regulated by the 1921 Convention relating to the Non-fortification of and Neutralisation of the Åland Islands. This book is the first to examine passage rights in the Åland Strait according to the Law of the Sea and its long history in times of war and peace.