Parents of US Citizens can apply for permanent resident status in the US as immediate relatives. Unlike most other immigrant candidates, no numerical limitation is placed on the number of US Citizens’ parents. And parents who applied belong to the IR-5 category among the candidates classification.
1. IR-5
Parents of US Citizens

2. General Case Procedure
First, file I-130 form along with other supporting documents to the USCIS. After that, the petitioner will receive I-797 approval notice and the USCIS will transfer the case to NVC (National Visa Center). For categories which do not need to wait for quotas like IR-5, NVC sends out fee payment bill once finished processing materials. After the payment, NVC will send out package 3.
Then, finish package 3 and send it back to NVC. NVC will transfer the case to US consulate appointed after background-check (If pass it, package 4 will be send to you). Around this time, the beneficiary needs to get medical examination and be prepared for the consulate interview.
Finally, if the interview goes well, the beneficiary will be approved to have his or her immigrant visa.

3. Qualifications
(1). Petitioner
① US citizen
② Age 21 or older
③ Have sufficient financial ability to support the intending immigrant parent(s)

(2). Beneficiary
Be qualified as a parent of the US Citizen.

4. Warnings
(1). A separate form must be filed for each eligible relative i.e. you can only apply for your father or your mother per person per time.
(2). Adopted children cannot petition for their biological parents since their relationship was terminated after the adoption.
(3). A stepparent qualifies for immigration on the basis of his/her relationship with his/her stepchild as long as the relationship was formed before the child’s 18th birthday.
(4). Adoptive parents qualify for immigration if the US Citizen child was adopted before the age of 16 and has lived with the adoptive parents in their legal custody for at least two years.