There are five major categories for Family Based Immigrant Visas. With the exception of the Immediate Relative category, there are limits on the number of visas that may be issued in each category each year. Each month the State Department published a Visa Bulletin, which states whether visas are available (current) in each respective category. You can determine whether a visa is available based on your priority date. In the family category, the priority date is the date your Petition for Alien Relative is filed with the INS.
Immigration based upon one's relationship to a U.S. citizen or Permanent Resident is categorized as follows: