Green card holders can, after a certain time, may apply for U.S. citizenship. Except in rare cases, no one can become a U.S. citizen without first receiving a green card. It is frequently said that green cards give all the benefits of U.S. citizenship except the rights to vote and hold public office. The differences between the two are actually greater. The most important distinction is that if you violate certain laws or abandon your U.S. residence, you can lose your green card. U.S. citizenship cannot be taken away, unless you acquired it fraudulently or voluntarily give it up. Another important difference is that U.S. citizenship allows you to petition for more of your family members to immigrate than a green card does, and their immigration will be faster.
Generally, an applicant for naturalization must be 18 years old or older at the time of filing, be a lawful permanent resident (have a “green card”).
The time period you have to wait before applying for U.S. citizenship ranges between three and five years– three years for people married to U.S. citizens, five years for everyone else. Asylees can actually apply four years after their approval for permanent residence, because their one year as an asylee counts, and refugees can apply five years after entry to the U.S., no matter when they became permanent residents.
(In some cases, this may be 18 months if you are married to a U.S. citizen.). Depending on your situation, there are different requirements that may apply to you.
Before applying for naturalization please keep in mind that if you have a parent that was a U.S. citizen, either by birth or naturalization, before you turned 18 years old, you may have a claim to citizenship.