What Does the Law Say?
The legal foundation that requires the inspection of all persons arriving in the United States comes from the Immigration and Nationality Act (INA), see INA § 235. Rules published in the Federal Register explain the inspection requirements and process. These rules are incorporated into the Code of Federal Regulations [CFR] at 8 CFR § 235.
What Can I Expect to Happen at a Port-of-Entry?
: Airport
When arriving at an airport, the airline will give all non-United States citizens a form to complete while still en route to the United States, either Form I-94 (white), Arrival/Departure Record, or Form I-94W (green), Nonimmigrant Visa Waiver Arrival/Departure Form. The forms ask for basic identification information and the address where you will stay in the United States.
Upon arrival, the airline personnel will show you to the inspection area. You will queue up in an inspection line and then speak with an Immigration Inspector. If you are a U.S. citizen, special lines may be available to you. If you are not a U.S. citizen, you should use the lanes marked for non-citizens.