The U.S. is an ever-increasing nation of immigrants. As of 2019, 15.2% of all individuals in the U.S. were foreign-born. Excluding tourism or unauthorized travelers, most of the people arriving in the U.S. with visas or green cards are temporary workers, students, or coming to be with their families.

Immigration to the U.S. occurs through a handful of channels housing a variety of visa categories. Family relationships, U.S. employers, and the need for humanitarian protection are the top channels for immigrants seeking temporary or permanent U.S. residence. In addition, individuals can come to the U.S. if they possess highly sought-after skills or are selected in a green-card lottery program. Visa categories have varying requirements, are subject to different numerical caps, and offer differing rights and responsibilities. Each of these channels has two main visa categories: permanent visas and nonimmigrant visas.

Beyond permanent admissions, the United States also admits workers, foreign students, and exchange visitors annually for temporary residence through a broad swath of visa categories, assigned to almost every letter of the alphabet. In most cases, these temporary workers can bring spouses and minor children with them and in some cases, will allow them to work. The most common temporary visa classifications include the B-1/B-2 for visitors, H-1B, TN, L-1 for temporary workers, and J-1 and F-1 for students.

The U.S. annually grants about 1 million green cards, approves nearly 7 million visas for temporary visitors, workers, students, and their families, and approves nearly 1 million people a year for U.S. citizenship. In addition, the U.S. allows approximately 20 million nationals from certain countries to enter the U.S. as temporary visitors for business or pleasure without obtaining visas from U.S. consulates abroad.