This article is from the FAQ, by with numerous contributions by others.
FAMILY SPONSORED PREFERENCES
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First Preference : Unmarried sons and daughters of U.S. citizens.
2A exempt second preference : spouse and unmarried children of permanent
residents - exempt from per-country limit.
2A subject second preference : spouses and unmarried children of permanent
residents - subject to per-country limit.
Legalization Beneficiaries - spouses and children (even though the marriage
took place after the date the petitioner was admitted to the U.S. as a
permanent resident.
2B second preference : Unmarried sons and daughters, 21 years of age or
older, of permanent residents.
Third Preference : married sons and daughters of U.S. Citizens.
Fourth Preference : Brothers and sisters of adult U.S. citizens.
EMPLOYMENT BASED PREFERENCES
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First Preference : Priority workers.
Second Preference : Professionals holding advanced degrees or persons
of exceptional ability.
Third Preference : Skilled workers and professionals.
Third Preference : Other workers (unskilled workers).
Fourth Preference : Certain special immigrants..
Fourth Preference : Certain religious ministers, professionals and other
religious workers.
Fifth Preference : Employment creation (investors).
Fifth Preference : Employment creation (investors in targeted employment
areas)
 
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