Who can apply for U.S. citizenship

Most people apply after five years as a lawful permanent resident (green card holder). These are the general requirements.

The general requirements

• Age: you are at least 18 years old when you file.
• Permanent residence: you have been a lawful permanent resident for at least 5 years, or 3 years if you have been married to and living with the same U.S. citizen for those 3 years and your spouse has been a citizen the whole time.
• Continuous residence: you have lived in the United States for that 5-year (or 3-year) period without long trips abroad that break your residence. A trip of 6 months or more can raise questions; a trip of a year or more usually breaks continuous residence.
• Physical presence: you were physically inside the United States for at least half of that time: 30 months of the 5 years, or 18 months of the 3 years.
• Local residence: you have lived for at least 3 months in the state or USCIS district where you apply.
• Good moral character during the required period.
• English and civics: you can read, write and speak basic English and pass the civics test, unless an exemption applies to you.
• Attachment to the Constitution: you are willing to take the Oath of Allegiance to the United States.

When you can file

You may send Form N-400 up to 90 days before you reach your 5-year or 3-year mark as a permanent resident. USCIS has an early filing date calculator.

Other paths

Different rules apply to people who served in the U.S. military, to some spouses of U.S. citizens working abroad, and to children of U.S. citizens, who may already be citizens. USCIS describes each path on its Learn About Citizenship pages.

Source: USCIS, I am a Lawful Permanent Resident of 5 Years and the Form N-400 page.