I can give you the general process. A U.S citizen can file an immigrant visa I-130 for his/her spouse, fiancee, children, son, daughter married and unmarried, parents, siblings. The I-130 petition is usually filed with the local BCIS (formerly INS) office. After approval this petition is forwarded to National Visa Center in New Hempshire. NVC completes certain requirements like Affidavit of support from the petitioner.  After that the file is forwarded to the overseas U.S embassy or consulate having jusrisdiction over the place of beneficiary's place of residence.  The Embassy then calls in the beneficiary for an interview and reviews all the local documentation as well. If every thing is in order an immigrant visa is issued.\n\nA green card holder can also file an immigrant visa petititon but only for spouse, children, unmarried sons and daughter.\n\nNow there are two basic categories one is called Immediate relative category and other one is preference category.  Immediate relative categories are not governed by any quota and all the applicants filing are processed e.g. spouse, children under 21 and parents of U.S citizen. All other categories are governed by a quota set by the federal government for each country per year. For example when a green card holder files a petition for the spouse the waiting period in this category is approximately 4 years.\n\nTo obtain further information on cutoff priority dates for preference categories check the following link:\n\nhttp://travel.state.gov/visa/frvi/bulletin/bulletin_1770.html