1. Immediate Relatives of U.S. Citizens

Immediate relatives include:

• spouses of U.S. citizens, including recent widows and widowers
• unmarried people under age 21 with at least one U.S. citizen parent
• parents of U.S. citizens, if the U.S. citizen child is at least age 21
• stepchildren and stepparents of U.S. citizens, if the marriage creating the stepparent/stepchild relationship took place before the child's 18th birthday, and
• adopted children of U.S, if the adoption took place before the child reached age 16.

An unlimited number of green cards are available for immediate relatives whose U.S. citizen relatives petition for them -- applicants can get a green card as soon as they get through the paperwork and application process. For more information, see Also see Fiancé & Marriage Visas: A Couple's Guide to U.S. Immigration, by Ilona Bray (Nolo).

2. Other Family Members

Certain family members of U.S. citizens or permanent residents are also eligible for green cards -- but not right away. They fall into the "preference categories" listed below, meaning that only a certain number of them will receive green cards each year (480,000). The system is first come, first served -- the earlier the U.S. citizen or permanent resident turns in a visa petition, the sooner the immigrant can apply for a green card. The waits range from approximately three to 24 years.

Family First Preference. Unmarried adults, age 21 or older, who have at least one U.S. citizen parent.

Family Second Preference. Section 2A: Spouses and unmarried children of a green card holder, so long as the children are younger than age 21. Section 2B: Unmarried children age 21 or older of a green card holder.

Family Third Preference. Married people, any age, who have at least one U.S. citizen parent.

Family Fourth Preference. Sisters and brothers of U.S. citizens, where the citizen is age 21 or older.

Also see How to Get a Green Card, by Ilona Bray (Nolo).

3. Preferred Employees and Workers

A total of 140,000 green cards are offered each year to people whose job skills are needed in the U.S. market. In most cases, a job offer is also required, and the employer must prove that it has recruited for the job and not found any willing, able, qualified U.S. citizens or residents to hire instead of the immigrant. Because of annual limits, this is a "preference category," and applicants often wait years for an available green card. Here are the subcategories:

Employment First Preference. Priority workers, including:

• persons of extraordinary ability in the arts, the sciences, education, business, or athletics
• outstanding professors and researchers, and
• managers and executives of multinational companies.

Employment Second Preference. Professionals with advanced degrees or exceptional ability.

Employment Third Preference. Professionals and skilled or unskilled workers.

Employment Fourth Preference. Religious workers and miscellaneous categories of workers and other "special immigrants" (described below)

Employment Fifth Preference. Investors willing to put $1 million into a U.S. business -- or $500,000 if the business is in an economically depressed area. The investor must also employ at least ten workers.

Also see U.S. Immigration Made Easy, by Ilona Bray (Nolo).

4. Green Card Lotteries: Ethnic Diversity

A certain number of green cards (currently 50,000) are made available to people from countries that in recent years have sent the fewest immigrants to the United States. Also see U.S. Immigration Made Easy, by Ilona Bray (Nolo).

5. Special Immigrants

Occasionally, laws are passed making green cards available to people in special situations. The current special immigrant categories are:

• clergy and other religious workers for legitimate religious organizations
• foreign medical graduates who have been in the United States since 1978
• former employees of the Panama Canal Zone
• foreign workers who were longtime employees of the U.S. government
• retired officers or employees of certain international organizations who have lived in the United States for a certain time
• foreign workers who were employees of the U.S. consulate in Hong Kong for at least three years
• foreign children who have been declared dependent in juvenile courts in the United States
• international broadcasting employees, and

• certain members of the U.S. Armed Forces who enlisted overseas and served 12 years.