Naturalization confers specific rights, some of them quite valuable. Citizens have voting privileges and protection in foreign countries. They have the right to cross the U.S. border at will and to sponsor family members for immigration who in turn can become eligible for citizenship. Since 1996, being a citizen also is a qualification for some government social programs.

In a broader sense, citizenship is a marker of integration into U.S. society. It makes a statement that an immigrant is here to stay. It is no surprise that citizenship rates are highest among immigrants who are far from their lands of birth, who own homes here and who are married to U.S. citizens. The general shift over the past decade from a declining naturalization rate to a rising one could signal a tipping point in the behavior of the nation’s latest wave of legal immigrants.

The U.S. is in the midst of its fourth great influx of foreign-born residents since the founding of the Republic. The first arrivals mainly were English and other western Europeans who settled in the early decades, seeking their fortunes or looking for political or religious freedom. They were followed in the mid-1800s by economic and political migrants, especially from Germany, Britain and Ireland, who helped settle the frontier.

The third group arrived from the late 1800s until 1914, when the outbreak of World War I restricted immigration. They included southern and eastern Europeans who moved mainly to urban areas, as well as immigrants from Asian nations who settled in western states. Immigration resumed briefly in 1920, but then a long period of restrictions took hold. Those limits began to relax after Congress passed legislation in 1965 that gave priority to immigrants with relatives in the U.S., who sponsored them for visas. This legislation, which helped instigate the fourth wave of immigrants, removed the country restrictions that tilted immigration toward Northern and Western Europe. It placed all countries on a more or less equal footing, which resulted in the first limits on Northern European immigration and permitted new immigrant flows from Asia.

That law, as well as conditions in sending countries, helped reshape the composition of the nation’s foreign-born population. Once primarily from Europe, the foreign-born population—naturalized citizens, legal immigrants, and unauthorized migrants—is now dominated by people born in Asia and Latin America.

The number of legal permanent resident admissions, which exceeded 1 million annually for some years this decade, has doubled since the late 1970s. As a result, the legal immigrant population has more than doubled in that time period to more than 24 million. At the same time, the unauthorized population, mostly immigrants from Mexico, also has risen sharply and now numbers more than 11 million. Immigration in-flows have subsided slightly from peaks in the late 1990s but remain high.

This report begins by discussing trends in legal immigration and naturalization in recent years, especially from 1995 to 2005, when the pace of naturalization picked up markedly. It presents results that illustrate the rising tendency on the part of legal immigrants to naturalize.

The next section explores the growth of both the foreign-born population and the naturalized-citizen population, with a discussion on countries of origin. Section three examines the characteristics of the naturalized population and of legal permanent immigrants who are eligible to naturalize and those who are soon to be eligible.

The last section analyzes which groups have been the most likely to naturalize, and how those tendencies have changed over time. It also compares countries of origin and regions to each other. Its analysis demonstrates that changes in behavior, not characteristics of the immigrant population, are driving up the naturalization rate.

The number of legal permanent residents who naturalize, and the proportion of those who do, still has room to grow. There are indications that it may: Legal immigration levels have topped 1 million per year several times this decade, creating a large pool of potential new citizens. And the fact that today’s authorized immigrants are taking fewer years to match their predecessors’ citizenship rates suggests that the proportion of those who eventually naturalize may rise above levels seen in the past.

In every era, the question of whether immigrants will become full-fledged members of society hangs in the air. A study of citizenship behavior offers a lens through which to look at this crucial issue. Theories abound over what causes the naturalization rate to rise or fall. This report does not address that question. [See Appendix A for a discussion on theories that try to explain why immigrants naturalize.]