There are five categories of employment based immigration:
1. First Preference (EB-1 priority workers): aliens with extraordinary ability, outstanding professors and researchers, and certain multinational executives and managers.
2. Second Preference (EB-2 workers with advanced degrees or exceptional ability): aliens who are members of the professions holding advanced degrees or their equivalent and aliens who because of their exceptional ability in the sciences, arts, or business will substantially benefit the national economy, cultural, or educational interests or welfare of the United States.
3. Third Preference (EB-3 professionals, skilled workers, and other workers): aliens with at least two years of experience as skilled workers, professionals with a baccalaureate degree, and others with less than two years experience, such as an unskilled worker who can perform labor for which qualified workers are not available in the United States.
4. Fourth Preference (EB-4 special workers such as those in a religious occupation or vocation): aliens who, for at least two years before applying for admission to the United States, have been a member of a religious denomination that has a non-profit religious organization in the United States, and who will be working in a religious vocation or occupation at the request of the religious organization.
5. Fifth Preference (EB-5 Employment Creation) If you would like to be granted immigrant status in the United States for the purpose of engaging in a new commercial enterprise, please see How Do I Become an Immigrant Through an Investment?.
Source:
http://www.uscis.gov