Immigration to the United States has been a major source of population growth and cultural change throughout much of the history of our nation. The economic, social, and political aspects of immigration have caused controversy regarding ethnicity, economic benefits, jobs for non-immigrants, settlement patterns, impact on upward social mobility, crime, and voting behavior. As of 2006, the United States accepts more legal immigrants as permanent residents than all other countries in the world combined. Since the removal of ethnic quotas in immigration in 1965, as called for by the Immigration and Nationality Act of 1965, the number of first- generation immigrants living in the United States has quadrupled, from 9.6 million in 1970 to about 38 million in 2007. In 2008, just over 1 million immigrants became naturalized as citizens of the United States.

            The cheap airline travel post-1960 facilitated travel to the United States, but migration remains difficult, expensive, and dangerous for those who cross the United States–Mexico border illegally. Approximately two-thirds of legal immigration to the US every year can be attributed to the reunification of families.

            The Immigration and Nationality Act of 1965, also known as the Hart-Cellar Act, equalized immigration policies. The result was an influx in new immigration from non-European nations. This drastically changed the ethnic make-up of the United States. Immigration doubled between 1965 and 1970, and again between 1970 and 1990. In 1990, George H. W. Bush signed the Immigration Act of 1990. This act raised the number of immigrants allowed within the United States each year.

            Recent debates on immigration have called for increasing enforcement of existing laws with regard to illegal immigration to the United States, building a barrier along some, or all, of the border between the United States and Mexico. Through much of 2006, the country and Congress was immersed in a debate about these proposals. Currently, few of these proposals have become law. A partial border fence was approved but was subsequently canceled.

            Contemporary immigrants tend to be younger than the native population of the United States, with people between the ages 15 and 34 substantially overrepresented. Immigrants are more likely to move to, and live in, areas populated by people with similar backgrounds. This phenomenon has held true throughout the history of immigration to the United States.

            Public attitudes about immigration in the U.S. have been heavily influenced by the aftermath of the September 11, 2001 attacks. After the attacks, the belief that immigration was beneficial to the United States became more scarce. More citizens are in favor of tighter controls on immigration, and they believe these changes would benefit our national security. Many of the major cities in America have a sanctuary policy. A policy of this nature protects illegal immigrants. These cities do not allow municipal funds or resources to be used to enforce federal immigration laws, usually by not allowing police or municipal employees to inquire about one's immigration status.