This book examines the lawfulness of the forced return of irregular migrants. Its central concern is the practice of sending individuals by force to countries of which they are not nationals and with which they often lack a meaningful connection. In addition to transit-country returns, the book analyses so-called “returns” to fourth countries, a misnomer used here to describe removals to states where the individual has never previously been present. Transit- and fourth-country arrangements are increasingly promoted by states in Europe and beyond as a response to unwanted migration, raising fundamental and unresolved questions under international and European law.