Immigration is the international movement of people to a destination country of which they are not natives or where they do not possess citizenship in order to settle as permanent residents or naturalized citizens. Commuters, tourists, and other short-term stays in a destination country do not fall under the definition of immigration or migration; seasonal labour immigration is sometimes included, however.

As for economic effects, research suggests that migration is beneficial both to the receiving and sending countries. Research, with few exceptions, finds that immigration on average has positive economic effects on the native population, but is mixed as to whether low-skilled immigration adversely affects low-skilled natives. Studies show that the elimination of barriers to migration would have profound effects on world GDP, with estimates of gains ranging between 67 and 147 percent for the scenarios in which 37 to 53 percent of the developing countries' workers migrate to the developed countries. Development economists argue that reducing barriers to labor mobility between developing countries and developed countries would be one of the most efficient tools of poverty reduction. Positive net immigration can soften the demographic dilemma in the aging global North.

The academic literature provides mixed findings for the relationship between immigration and crime worldwide, but finds for the United States that immigration either has no impact on the crime rate or that it reduces the crime rate. Research shows that country of origin matters for speed and depth of immigrant assimilation, but that there is considerable assimilation overall for both first- and second-generation immigrants.

Research has found extensive evidence of discrimination against foreign-born and minority populations in criminal justice, business, the economy, housing, health care, media, and politics in the United States and Europe.