Form N-400 is the official form of application for citizenship. The N-400 can
be downloaded from the Citizenship and Immigration Service (USCIS) website. Visiting this site, you should carefully read the instructions for completing it and get acquainted with the list of the required documents. One single mistake can become a reason for a re-submission — be very attentive. Besides it, you can fill in the required forms at https://usimmigrationforms.com/. The service specialists carefully prepare immigration forms and always check them for errors.