The U.S. immigration system is complex and can be difficult to understand. These resources provide key data points, historical information, and background on hot topics in immigration. Learn the basics about immigration. Immigration in the United States is complex and ever-evolving. Start here to understand the fundamental aspects of immigration policy, its history, and its impact on both individuals and the country at large. Learn commonly used terms about immigration law and how the U.S. immigration system is designed. Explore layered topics like how and whether immigrants can become citizens, as well as what individual protections look like under the law.