Spouse of a U.S. citizen; parent or step-parent of a U.S citizen; child or stepchild under the age of 21 of a U.S. citizen and spouse of a deceased U.S. citizen . Note: A step-parent or child will qualify for immigration only if the marriage creating the step parent/child relationship occurs before the child’s eighteenth birthday.

Unmarried son/daughter (aged 21 or over) of a U.S. citizen; married son/daughter of a U.S citizen; brother/sister of a U.S. citizen; spouse and unmarried son or daughter of a Lawful Permanent Resident (LPR).

A widow/widower of a U.S. citizen may file an immigrant visa petition, form I-360 (PDF – 230 kb), on his/her own behalf in the immediate relative category if he/she had been married to the deceased U.S. citizen, was not legally separated at the time of death and has not remarried. To qualify, the petition must be filed with the United States Citizenship and Immigration Services (USCIS) or a U.S. Embassy within two years of the death of the U.S. citizen.

You can find more information pertaining to the widow/widower of a U.S. citizen on the USCIS website.

Persons seeking to immigrate in one of the family based preference categories will qualify for immigrant status only if they have the necessary relationship to a U.S. citizen or Lawful Permanent Resident as described below.

Note:
Grandparents, aunts, uncles, in-laws and cousins cannot sponsor a relative for immigration.