Form I-140, Immigrant Petition for Alien Worker is a form submitted to the United States Citizenship and Immigration Service (USCIS) by a prospective employer to petition an alien to work in the US on a permanent basis.

Form I-129, Petition for a Nonimmigrant Worker is a form submitted to the United States Citizenship and Immigration Services used by employers or prospective employers to obtain (or amend the details of) a worker on a nonimmigrant visa status.

Form N-400 is used to apply for US citizenship through the naturalization process. Lawful permanent residents (also known as green card holders) of the United States, who meet the eligibility requirements, can file N-400 form to request citizenship.