This book focuses on current frontier-related issues such as humanitarian crises, economic crises, discrimination of migrants in certain countries, different typologies of borders such as land, maritime, air, space, and even cyberspace borders, and environmental protection of water resources at borders. It addresses legal and theoretical considerations and presents empirical cases showing the manifestations of the concept in the real world and its dynamics. Without claiming to exhaust the debate on frontiers, especially given the breadth of the subject and the large number of viewpoints from which the phenomenon can be examined, this book intends to be a helpful source of insights for academics, university students, and others who wish to explore the complex and multifaceted worlds that emerge, particularly in a globalized society, from the interaction between the various actors and scenarios that shape the reality of frontiers.