More than 100,000 years ago, the first modern humans left Africa and began to colonize the world. Since then, human history is also a history of migration. Migration has always been a strong impetus towards human development. These days, however, migration is often seen as a problem or threat. But what exactly is migration? What are its underlying causes? And what problems and opportunities does migration present? Migration is defined as the permanent change of residents of a person or group. It is a natural social phenomenon. Humans have colonized the entire world and penetrated its remotest areas. Migration has taken place within very different contexts. Military conquest, flight of refugees, expulsion, or enslavement. Migrants have also traveled in search of economic opportunities, new settlement areas, or trade routes. Currently, approximately 216 million people are living away from their place of birth. This number equals about 3% of the world population. Analyzing the reasons for migration, one distinguishes between push and pull factors. Often, both appear together. Push factors are circumstances in the country of origin that lead people to emigrate. For example, poverty, war, or environmental disasters. Pull factors are conditions in the destination country that make immigration attractive, such as economic opportunity and political freedom. Considering these reasons, one distinguishes between different forms of migration. Asylum seekers are fleeing war or persecution in their home country. With internationally accepted Geneva Convention states, no person may be sent back to a country where they face inhumane treatment, torture, or the death penalty. Labor migration is based on the hope for a better economic future. But it can be difficult for people from poor countries to get a work or residence visa in a rich country. Migrants who enter the destination country in an informal way, or who do not leave the country after the expiration of a tourist visa, are referred to as illegal migrants. Another case is the international migration of highly trained professionals. It takes place, both between developed countries and between developing and developed countries. This form of migration is often desired and encouraged by the destination countries. What are the main migration routes today? By far, most immigrants live in the United States, followed by Russia and Germany. The main countries of origin are Mexico, India, China, and Russia. In proportion to their population, Persian Gulf countries host the largest share of migrants, about 35% of their population. They mostly come from South Asia and Egypt. Most migrants in the US come from Latin America, particularly from Mexico. In Europe, the origin of immigrants differs considerably between countries and reflects their historical development. In Germany and Denmark, a large share of migrants are of Turkish origin. Most immigrants in France, Portugal, and Spain come from their former colonies. In addition, there is a strong migration within Europe. This is promoted by the EU's principle of free movement. Citizens of the EU are allowed to live in any EU member state without restrictions. Nowadays, migration is often seen as a threat. This is caused by a number of fears. For example, the idea that immigrants are expensive and a burden to the welfare system of the destination country. Especially in host countries that offer few opportunities of social mobility to migrants, they are usually the most vulnerable parts of society. Another fear is that the host country will lose what is perceived as its national identity, especially through the influx of groups from other religions or cultures. Often, there is no successful integration strategy, so different ethnic groups live in separate neighborhoods. As a result of these fears, the migration policies in Western industrial countries have become increasingly restrictive. The US has built a giant fence with high-tech surveillance to seal its southern border with Mexico. The European Union is also fortifying its borders. Migration is perceived primarily as a security problem. The EU is trying to block migrants before they reach its territory. This is done by bilateral agreements with the departure and transit countries, and an ever-increasing control of refugee routes on land and water. In 2004, the EU established Frontex, a joint agency to coordinate the surveillance and closure of its external borders. Human rights groups point out that many refugees with a legitimate claim for asylum are blocked this way. It is increasingly difficult to reach Europe. The result is that migration attempts are getting more and more risky and often end disastrously. According to conservative estimates between 1988 and 2010, approximately 15,000 people died attempting to reach the EU. More people than at any other border in the world. What is not considered most of the time, migration also has positive aspects. Migration contributes to the economic development in migrants' countries of origin. Migrants around the world transfer over $300 billion to their home country each year. That is considerably more than the official development assistance to these countries. In European countries, as well as in other industrialized nations, such as Japan, the birth rate has dropped to a low level below the replacement rate. The result, declining population and an aging society. Experts believe that Europe will soon be heavily dependent on migration in order to meet its employment needs and to stabilize the retirement system. Finally, migration contributes to the cultural diversity of destination countries. We see that the debate over migration is burdened by fear and prejudice. The effect is a restrictive immigration policy and strict efforts to prevent migration to destination countries. This is not just a problem in terms of ethics, but also politically and economically questionable. In order to deal with the problems attached to migration, it is especially important to develop and implement a constructive migration policy. Such a policy would include regulated immigration, as well as provide rights for legitimate asylum seekers.