Certain rules apply to all the family-based green card categories alike: the sponsor, or “petitioner”, must have a domicile (principal residence) in the United States, and must demonstrate the ability to support the sponsored foreign relative, or “beneficiary”, financially.
Visas for Immediate RelativesThe Immediate Relative category includes the spouse, parent, or unmarried child under 21 of a U.S. citizen. Children under 21 are ineligible to petition for a parent. Visas in the Immediate Relative category are always current; there is no preference category backlog. No derivative beneficiaries are allowed - a separate petition is required for any dependents. For example, if the sponsored immigrant spouse has a minor child from a prior marriage, the sponsoring US spouse must file a separate petition for that child. If an Immediate Relative petition is filed by the US citizen on behalf of a spouse, and they have been married for less than two years when the case is granted, the foreign spouse will get "Conditional Residence," valid for only two years. Then, the US and foreign spouse will have to file another petition, in the 90 days prior to that two-year expiration date of conditional residence, to remove the conditions on residence.
First Preference The Family-Based First Preference, F1, includes the unmarried son or daughter over age 21 of a U.S. citizen. Second Preference The Family-Based Second preference is subdivided into two sub-groups with different visa availability. The F2A category includes the spouse or minor child under 21 of a Lawful Permanent Resident. The F2B category is for the unmarried adult son or daughter of a Lawful Permanent Resident. Third Preference The Family-Based Third Preference category, F3, is for the married son or daughter of a U.S. citizen. Fourth Preference The Family-Based Fourth Preference, F4, is for the brother or sister of a U.S. citizen. Changes in the applicable family immigrant visa category can occur automatically, by operation of law, when events in the life of the U.S. petitioner or the foreign beneficiary change the facts underlying an immigrant visa petition. Per “automatic conversion of preference classification” under 8 CFR §204(i), this may happen in the following situations: (1) By a change in the beneficiary’s marital status. (2) By the minor beneficiary reaching age 21. (3) By the petitioner’s naturalization to U.S. citizen. In addition to these family-based immigrant visas, there are some temporary “nonimmigrant visas” based on family relationships. These are the K-1, for fiancée of a U.S. citizen, K-2 for minor child of a fiancée, the K-3 spouse of a US citizen with a pending immigrant visa petition (only where the foreign spouse resides abroad, and the marriage occurs outside the U.S., in the home country abroad), and K-4, for the minor child of a K-3 spouse. Although the Ks are technically nonimmigrant visas, they are quasi-immigrant hybrid visas, and are treated the same as immigrant visa applications insofar as: -they require an I-864 Affidavit of Support by the sponsor, & a medical examination of the K visa applicant by a panel physician designated by the US Embassy -all applicants over 16 must provide police clearances from all countries they have lived in outside the US -waivers of inadmissibility will be treated as immigrant waivers | 
