One of the most widely used methods to obtain legal permanent residence in the U.S. is through an employment-based immigrant visa petition, which allows for five classifications commonly referred to as preferences.
EB-1: First Preference, Priority Workers
EB-2: Second Preference, Professionals with Advanced Degrees or Persons with Exceptional Ability
EB-3: Third Preference, Skilled or Professional Workers
EB-4: Fourth Preference, Special Immigrants
EB-5: Fifth Preference, Immigrant Investors