Migration has played a central role in society throughout the ages. It has contributed to foster economy, to disseminate and to create new cultures, languages and even civilizations. However, the 20th century has presented anew array of challenges to migratory processes, especially when public policies tended to impose quotas over international migrants and internal migration was associated with marginalization in urban areas. In this arena, where migration has often been divided into good or bad for a country or region and new public policies around visas for international migrants have arisen, another issue has emerged with greater strength in the beginning of the new century: environmental hazards have prompted large groups of people to flee from their homes and seek refuge in places where they can find minimum safety.