A more thorough explanation:

Definition: Immigration law refers to the laws and regulations that govern the entry and exit of people from one country to another. In the United States, immigration law is primarily dealt with at the federal level and determines who may enter, how long they may stay, and when they must leave. It also provides the means by which certain aliens can become legally naturalized citizens with full rights of citizenship.

Examples: The Immigration and Nationality Act of 1952 eliminated all race-based quotas, replacing them with purely nationality-based quotas. The Immigration Reform and Control Act of 1986 toughened criminal sanctions for employers who hired illegal aliens, denied illegal aliens federally funded welfare benefits, and legitimized some aliens through an amnesty program. The Illegal Immigration Reform and Immigrant Responsibility Act of 1996 revolutionized the process of alien entry into the United States.

Explanation: These examples illustrate how immigration law has evolved over time in the United States. The Immigration and Nationality Act of 1952 eliminated discrimination based on race, while the Immigration Reform and Control Act of 1986 aimed to curtail illegal immigration. The Illegal Immigration Reform and Immigrant Responsibility Act of 1996 changed the process of alien entry into the United States by replacing the term "entry" with "admission" and requiring all applicants to submit to an inspection by U.S. customs.