American immigration (emigration to the Unite States of America) refers to the movement of non-residents to the United States. Even though the foreign born have never composed more than 16% of the U.S. population since 1675 , immigration has been a major source of population growth and cultural change throughout much of American history. The economic, social, and political aspects of immigration have caused controversy regarding ethnicity, religion, economic benefits, job growth, settlement patterns, impact on upward social mobility, levels of criminality, nationalities, political loyalties, moral values, and work habits. As of 2006, the United States accepts more legal immigrants as permanent residents than any other country in the world. In 2006, the number of immigrants totaled 37.5 million.