A person who is spouse of a US citizen or a permanent resident is eligible to apply for permanent resident status. Spouses of US citizens belong to the category of IR-1(the marriage has lasted for over 2 years) or CR-1(the marriage has lasted less than 2 years) while spouses of US permanent residents belong to the category of F-2A. No numerical limitation is placed on the IR-1 or CR-1 categories. Unfortunately, F-2A category has numerical limitation.

1. IR-1/CR-1,F-2A
IR-1: an alien who has been married to a US citizen more than 2 years
CR-1: an alien who has been married to a US citizen less than 2 years, who will gain conditional permanent residency for 2 years.
F-2A: an alien who qualifies as the spouse of a US permanent resident

2. Qualification
(1). Petitioner
① US citizen or legally permanent resident
② Have sufficient financial ability to support the intending immigrant spouse

(2). Beneficiary
Be qualified as a spouse. A spouse is a legally wedded husband or wife. Merely living together does not qualify for immigration. Common-law spouses may qualify as spouses for immigration only if the law of the country where the common-law marriage occurs recognizes common-law marriages and grant the couple the same rights and obligation as in a traditional one. In case of polygamy, only the first spouse may qualify as a spouse for immigration.

3. 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, NVC sends out fee payment bill once finished processing materials. For categories which need to wait for quotas, NVC sends out Visa fee payment bill when the petitioner's priority date is close to becoming current. 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.

4. Filing Material
(1). Application Letter
(2). I-130 form
(3). G-325A
(4). Filing Fee
(5). Supporting Documents
① Petitioner
A copy of birth certificate, a copy of Form FS-240, a copy of unexpired US passport
② Beneficiary
A copy of unexpired passport, photo, a certified copy of foreign Birth Certificate
③ Documents to Prove Relationship
A copy of your marriage certificate, divorce decree, documentation showing joint ownership or property, a lease showing joint tenancy of a common residence, joint credit card statement, joint bank statement, utility bills, airline tickets or boarding passes you traveling together and so on.

5. Tips
(1). Termination of all previous marriages. U.S. law does not allow polygamy. If you were married before, you and your spouse must both show that you ended (terminated) all previous marriages before your current marriage. The death and divorce documents that show termination of marriages must be legal and verifiable in the country that issued them. Divorces must be final. In cases of legal marriage to two or more spouses at the same time, or marriages overlapping for a period of time, you can file only for your first spouse.
(2). Within 90 days before the second anniversary as a conditional resident, the alien spouse need to jointly petition to remove the conditions on the residency. Failure to do so will result in the termination of the alien spouse's conditional permanent residence.
(3). The children of US Citizen's spouse do not have derivative status in an immediate relative (IR) petition. This is different from the family second preference (F-2) petition. A child is included in his/her parent's F-2 petition. A child is not included in his/her parent's IR petition. If you are a U.S. citizen, you must file separate immigrant visa petitions for each of your children.
(4). The spouse and minor children of second preference immigrants (F-2A) can immigrate with them. The spouse and children of the principal alien are entitled to derivative classification and they are charged against the visa allotment for the same preference as the principal alien.
(5). Battered spouses of permanent resident may also file their own immediate relative petitions. Any credible evidence submitted with the spousal petition with regard to the treatment of the alien spouse will be considered by the USCIS.