This report is a chart book of selected immigration trends. Key immigration issues that Congress has considered i n recent years include increased border security and immigration enforcement, expanded employment eligibility verification, reforms to the system for legal temporary and permanent immigration, and options to address the millions of unauthorized aliens residing in the country. The report offers snapshots of time series data, using the most complete and consistent time series currently available for each statistic . The key findings and elements germane to the data depicted are summarized with the figures. Some of the time series span decades, while others capture only a few years. For those who seek more complete analyses of the issues, the report cites Congressional Research Service (CRS) products that discuss the policies underlying the data presented in each figure. Much of the data come from administrative sources, typically the Department of Homeland Security (DHS) and the Department of State (DOS). For historical context, demographic data from the U.S. Census Bureau are also included. The Immigration and Nationality Act (INA), which was first codified in 1952, contains the provisions detailing the requirements for admission (permanent and temporary) of foreign nationals, grounds for exclusion and removal of foreign nationals, document and entry-exit controls for U.S. citizens and foreign nationals, and eligibility rules for the naturalization of foreign nationals. Congress has significantly amended the INA several times since 1952, most notably by the Immigration Amendments of 1965, the Refugee Act of 1980, the Immigration Reform and Control Act (IRCA) of 1986, the Immigration Act of 1990, and the Illegal Immigration Reform and Immigrant Responsibility Act (IIRIRA) of 1996. Legal immigration encompasses permanent admissions (e.g., employment-based or family-based legal permanent residents (LPRs)) and temporary admissions (e.g., guest workers, foreign students). This chart book presents historical time series data on permanent admissions as well as a breakdown of legal permanent residents by broad classes of admission. Trends in temporary admissions, including legal employment-based temporary migrants, are also depicted. Immigration control encompasses an array of enforcement tools, policies, and practices to secure the border and to prevent and investigate violations of immigration laws. Among the statistical trends tracking immigration control presented are inadmissibility determinations, border apprehensions, worksite enforcement prosecutions, and alien removal. The final section of this chart book looks at recent trends in the unauthorized resident alien population and unaccompanied alien children. Immigration to the United States was peaking at the beginning of the 20 th century. In 1910, foreign-born residents made up 14.8% of the U.S. population. Immigration dropped as a result of the numerical limits and national origins quotas imposed by the Immigration Acts in 1921 and 1924. Levels fell further during the Great Depression and World War II. The annual number of settled immigrants, typically referred to as LPRs, rose gradually after World War II ( Figure 1 ). In 1952, the INA was codified and, as amended, remains the governing statute. The growth in immigration after 1980 is partly attributable to the total number of LPRs entering through the preference system as well as immediate relatives of U.S. citizens. The Immigration Reform and Control Act (IRCA) of 1986 enabled 2.1 million unauthorized aliens residing in the United States as of 1982 to become LPRs. In addition, the number of refugees admitted increased from 718,000 in the period 1966-1980 to 1.6 million during the period 1981-1995, after the enactment of the Refugee Act of 1980. The Refugee Act established permanent provisions for refugees and asylees to become LPRs. The Immigration Act of 1990 was the last significant revision of legal permanent immigration. It set a statutory worldwide level of 675,000 LPRs annually, but certain categories of LPRs, most notably immediate relatives of U.S. citizens and refugees, are permitted to exceed the limits. The INA further holds countries to an annual numerical limit of 7% of the worldwide level of U.S. immigrant admissions, known as per-country limits or country caps. Immigration to the United States today has reached levels comparable to the early years of the 20 th century. In FY2013, 990,553 aliens became LPRs through admissions (459,751) or status adjustments (530,802). For further background and analysis, see CRS Report R42866, Permanent Legal Immigration to the United States: Policy Overview . In any given period of U.S. history, a handful of countries have dominated the flow of immigrants, but the dominant countries have varied over time. Figure 2 presents trends in the top immigrant-sending countries (together comprising at least 50% of the immigrants admitted) for selected decades. The Immigration Act of May 19, 1921, imposed the first numerical limits on LPR admissions to the United States, and it set the level of admission of aliens from specific countries to 3% of the foreign-born persons of that nationality who lived in the United States in 1910. A few years later, the Immigration Act of May 26, 1924, established the national origins system, which set quotas based on the number of foreign-born persons of that nationality in the country in 1890 and 1920. Both laws exempted Western Hemisphere countries from the limits. The Immigration Amendments of 1965 replaced the national origins quota system with per-country ceilings. Figure 2 illustrates that immigration over the last few decades of the 20 th century was not as dominated by three or four countries as it was earlier in the century. Although Europe was home to the countries sending the most immigrants during the early 20 th century (e.g., Germany, Italy, Austria-Hungary, and the United Kingdom), Mexico has been a top sending country for most of the 20 th century—largely after 1970—and into the 21 st century. Other top sending countries from FY2001 through FY2010 were the Dominican Republic, El Salvador, Colombia, and Cuba (Western Hemisphere); and the Philippines, India, China, South Korea, and Vietnam (Asia). These data suggest that the per-country ceilings established in 1965 had some effect. As Figure 2 illustrates, immigrants from only three or four countries made up more than half of all LPRs prior to 1960. By the last two decades of the 20 th century, immigrants from seven to eight countries comprised about half of all LPRs, and this pattern has continued into the 21 st century. For further background and analysis, see CRS Report R42866, Permanent Legal Immigration to the United States: Policy Overview . The total number of foreign-born residents in the United States is at the highest level in U.S. history. In the past 50 years, the number of foreign-born residents of the United States has gone from just under 10 million in 1960 to 42 million in 2014 ( Figure 3 ), a 338% increase. The foreign born represented 13.3% of the U.S. population in 2014, approaching a level not seen since the proportion of foreign-born residents reached 14.8% in 1910. As part of this increase, the source regions of foreign-born residents have shifted from Europe (75% in 1960) to Latin America and Asia (82% in 2014). Between 2000 and 2014, the foreign born contributed 30% of the total U.S. population increase. Foreign-born residents comprised most of the increase in the prime 25-54 working age population over this decade. Almost one-third of current foreign-born residents arrived in the United States since 2000, as discussed in the CRS report cited below. The DHS Office of Immigration Statistics (OIS) has estimated that as of January 1, 2013, about 13.1 million foreign-born residents (32% of all foreign born in 2013) were LPRs. OIS has also estimated that as of January 1, 2012, about 1.9 million foreign-residents (5% of all foreign born in 2012) were legally present on long-term temporary visas and about 11.4 million (28% of all foreign born in 2012) were aliens residing in the United States without legal authorization. DHS estimates for these populations in more recent years are not yet available. For further background and analysis, see CRS Report R41592, The U.S. Foreign-Born Population: Trends and Selected Characteristics . The INA specifies a complex set of numerical limits and preference categories that give priorities for permanent immigration based on family relationships, employment connections, protection of refugees, and diversity of admissions by country of origin. Apart from aliens legalized by IRCA, the largest growth since 1986 has been in the immediate relatives of U.S. citizens, almost doubling from 223,468 in FY1986 to 439,460 in FY2013, as presented in Figure 4 . Statutory changes from the Immigration Amendments Act of 1990 increased the number of employment-based immigrants from 56,617 to 161,110 over the same period. About 87% of the employment-based LPRs adjusted from a temporary status. The employment-based numbers include the accompanying spouses and children of the qualifying LPR. In FY2013, about 991,000 aliens became LPRs ( Figure 5 ). Of this total, 65% entered on the basis of family ties. Other major categories were employment-based LPRs (16%), diversity immigrants (5%), and refugees and asylees (12%). For further background and analysis, see CRS Report R42866, Permanent Legal Immigration to the United States: Policy Overview . The pool of people who are potentially eligible to immigrate to the United States as LPRs each year typically exceeds the worldwide level set by the INA. Figure 6 presents a snapshot of this pool on November 1, 2015.