Immigration refers to the movement of people among countries. While the movement of people has existed throughout human history at various levels, modern immigration implies long-term permanent residence. Short-term visitors and tourists are considered non-immigrants (see expatriate). Immigration across national borders in a way that violates the immigration laws of the destination country is termed illegal immigration. Under this definition, an illegal immigrant is a foreigner who either illegally crossed an international political border, whether by land, water, or air, or a foreigner who legally entered a country but overstays his/her visa_(document) in order to live and/or work therein. Seasonal labour migration, while generally non-permanent in nature (typically for periods of less than a year), is often treated as a form of immigration.

The modern concept of immigration is related to the development of nation-states and nationality law. Citizenship in a nation-state confers an inalienable right of residence in that state, but residency of non-citizens is subject to conditions set by immigration law. The emergence of nation-states made immigration a political issue: by definition it is the homeland of a nation defined by shared ethnicity and/or culture.

The global volume of immigration is high in absolute terms, but low in relative terms. The International Integration and Refugee Association estimated 190 million international migrants in 2005, about 3 percent of global population. The other 97 percent still live in the country in which they were born.Fact: date=February 2008 The Middle East, some parts of Europe, small areas of South East Asia, and a few spots in the West Indies have the highest percentages of immigration population recorded by the UN Census 2005.

Following Poland's entry into the EU in May 2004 it is estimated that by the start of 2007 375,000 Poles have registered to work in the UK, although the total Polish population in the UK is believed to be 750,000. Many Poles work in seasonal occupations and a large number are likely to move back and forth including between Ireland and other EU Western nations.

According to Eurostat, Some EU member states are currently receiving large-scale immigration: for instance Spain, where the economy has created more than half of all the new jobs in the EU over the past five years. The EU, in 2005, had an overall net gain from international migration of +1.8 million people. This accounts for almost 85% of Europe's total population growth in 2005. In 2004, total 140,033 people immigrated to France. Of them, 90,250 were from Africa and 13,710 from Europe. In 2005, immigration fell slightly to 135,890. In recent years, immigration has accounted for more than half of Norway's population growth. In 2006, Statistics Norway's (SSB) counted a record 45,800 immigrants arriving in Norway — 30% higher than 2005. At the beginning of 2007, there were 415,300 persons in Norway with an immigrant background (i.e. immigrants, or born of immigrant parents), comprising 8.3 per cent of the total population.