The crossing of national state borders is one of the most-discussed issues of contemporary times and it poses many challenges for individual and collective identities. This book examines the three constitutive parts discerned in the cross-border mobility decision-making process: people, borders and trajectories and their interrelationships. Illustrated by a global range of case studies, it demonstrates that the relation between the three is not fixed but flexible and that decision-making contains aspects of belonging, instability, security and volatility affecting their mobility or immobility.