If you have U.S. lawful permanent residence, then you will have been issued a photo identity card to prove your status, known as a "green card." That card has an expiration date. The time allotted before your card expires is ten years. After this time has passed, the green card holder is expected to renew the card (using Form I-90, issued by U.S. Citizenship and Immigration Services or USCIS).
But what if you are in the process of applying for U.S. citizenship when the green card expires?
It's Possible to Apply for Citizenship With an Expired Green Card
A green card is merely evidence of your status. You are still a permanent resident, even if your green card has expired. On that basis, many people have chosen to simply apply for U.S. citizenship after their green card has expired, or not bother to renew the green card if it expires while they're waiting for a USCIS decision on their citizenship application. USCIS policy goes back and forth on how accepting it is of this practice, but lack of a renewed green card should not, by itself, hold up your naturalization approval.
Note: This discussion does not apply to people with conditional, not permanent residence. The expiration date on a conditional green card means not only the expiration of the card, but the expiration of your status. You must convert from conditional residence to permanent residence, and spend some years as a permanent resident, before applying for U.S. citizenship.
It's Safer to Renew Your Green Card Even if You're Applying for Citizenship
In general, you are expected to carry a valid green card with you at all times, as one of the responsibilities of being a permanent resident. Meqnwhile, applying for citizenship or naturalization can be a months-long process. (The exact timeline depends on the office at which you apply.) Spending all that time without a green card could make it difficult to gain employment (or prove your status to your current employer) and to reenter the United States if you travel abroad.
If you really don't want to renew, then you're on safest ground if the date that you apply for citizenship is more than six months prior to the date your green card will expire.
