Family. Relatives of U.S. citizens are given top priority, and are eligible to file green card petitions. "Immediate family" is defined, in order of priority, as spouses (including recent widows), unmarried children under 21, parents of citizens, some stepchildren and stepparents, and adopted children (if the adoption took place before the child turned 16). Non-immediate family members may also petition, though the process may be slower.
Workers. Like the "family" category, job-based eligibility for green cards is also broken down into a priority list. Preference is usually given to those workers who have special, unique or advanced skills. Other workers that may qualify can include professionals with advanced degrees or extraordinary ability, or skilled workers and those holding religious jobs.
Green card "lottery" winners. The U.S. government usually makes a limited number of green cards available each year through a lottery that is designed to promote ethnic diversity. These lotteries give preference to those who are from countries that have the least number of immigrants coming over to the United States.
Asylum. Some immigrants may qualify for green cards if they seek asylum and refuge in the United States. Those who seek asylum and refuge are often those subject to persecution on the basis of a protected category such as race, nationality, religion, or political stance.