In order to distinguish between those who may and may not enter or leave, states everywhere have developed extensive systems of identification, central to which is the passport. This innovative book argues that documents such as passports, internal passports and related mechanisms have been crucial in making distinctions between citizens and non-citizens. It examines how the concept of citizenship has been used to delineate rights and penalties regarding property, liberty, taxes and welfare. It focuses on the US and Western Europe, moving from revolutionary France to the Napoleonic era, the American Civil War, the British industrial revolution, pre-World War I Italy, the reign of Germany's Third Reich and beyond. This innovative study combines theory and empirical data in questioning how and why states have established the exclusive right to authorize and regulate the movement of people.