What Is Form N-400?

Form N-400, the Application for Naturalization, is the official USCIS form used by eligible permanent residents to apply for U.S. citizenship. Filling it out accurately is critical — errors or omissions can delay your case or result in a Request for Evidence (RFE).

This guide walks you through every major section of the form so you can complete it with confidence.

Before You Begin: Eligibility Checklist

Make sure you meet the basic requirements before submitting Form N-400:

  • You are at least 18 years old
  • You have been a Lawful Permanent Resident (LPR) for at least 5 years (or 3 years if married to a U.S. citizen)
  • You have maintained continuous residence in the U.S.
  • You have been physically present in the U.S. for at least 30 months out of the past 5 years
  • You can read, write, and speak basic English
  • You have good moral character

Part-by-Part Breakdown of Form N-400

Part 1 – Information About Your Eligibility

Select the basis for your eligibility. The most common selections are being a permanent resident for 5 years, or 3 years if your spouse is a U.S. citizen. Choose only one option and make sure it accurately reflects your situation.

Part 2 – Information About You

Provide your full legal name exactly as it appears on your Green Card. If you want to legally change your name through naturalization, this section allows you to request that. Double-check your Alien Registration Number (A-Number) — it appears on the front of your Green Card.

Parts 3 & 4 – Residence and Contact Information

List your current and previous addresses for the last 5 years. Every address matters, including temporary stays. Gaps in address history are a common source of RFEs.

Part 5 – Information for Criminal Background Check

Enter your physical description accurately. USCIS uses this for biometrics and identity verification.

Part 7 – Time Outside the United States

List every trip outside the U.S. lasting 24 hours or more during the past 5 years. Include destination, departure date, return date, and purpose. Failing to disclose trips is one of the most common mistakes applicants make.

Part 8 – Marital History

Disclose all marriages, including divorced or annulled ones. USCIS cross-references this with tax records and other federal databases.

Part 12 – The Good Moral Character Section

This is perhaps the most sensitive section. Answer every question truthfully — even if you think something is too minor to mention. Lying on a federal application is far more damaging than disclosing a past issue. If you have any criminal history, consult an immigration attorney before submitting.

Supporting Documents to Include

  • A copy of both sides of your Permanent Resident Card (Green Card)
  • Passport photos (2 identical photos, 2"x2")
  • Filing fee payment (check current fees on the USCIS website)
  • Marriage certificate (if applying under the 3-year rule)
  • Divorce decrees for any prior marriages
  • Copies of tax returns (if applicable)

Where to File

You can file Form N-400 online through your USCIS online account or by mail to the appropriate USCIS lockbox facility based on your state of residence. Filing online allows you to track your case more easily and receive electronic notifications.

After You Submit

After USCIS receives your application, you will typically receive:

  1. A filing receipt notice (Form I-797)
  2. A biometrics appointment notice
  3. An interview appointment notice
  4. A decision on your application

Processing times vary by field office. Check the USCIS Case Status portal regularly using your receipt number to stay updated.

Final Tips

  • Use black ink if filing a paper form
  • Never leave a field blank — write "N/A" if not applicable
  • Keep a complete copy of your entire application package
  • Use the most current version of the form (check USCIS.gov before filing)