This book provides a philosophical defence of open borders. Two policy dogmas are the right of sovereign states to restrict immigration and the infeasibility of opening borders. These dogmas persist in face of the human suffering caused by border controls and in spite of a global economy where the mobility of goods and capital is combined with severe restrictions on the movement of most of the world’s poor. Alex Sager argues that immigration restrictions violate human rights and sustain unjust global inequalities, and that we should reject these dogmas that deprive hundreds of millions of people of opportunities solely because of their place of birth. Opening borders would promote human freedom, foster economic prosperity, and mitigate global inequalities. Sager contends that studies of migration from economics, history, political science, and other disciplines reveal that open borders are a feasible goal for political action, and that citizens around the world have a moral obligation to work toward open borders.