What immigration and naturalization service form is used to apply to become a natuarilized citizen?

Form N-400 is the application that is used to get naturalized as a US citizen. For this, the applicant should first become a permanent resident ( Green card Holder) and should be above 18 yrs of age. Apart from this, they need to meet several other criteria also.

N-400 should be submitted with all the supporting documents and photographs at the ASC that has jurisdiction over their area.