The Immigration Act of 1990 created the Diversity Immigrant Visa Lottery, a program that provides 50,000 green cards to citizens of countries that sent the least number of immigrants to the U.S. in the preceding five year period.
The list of eligible countries changes each year depending upon how many immigrants came to the U.S. from a particular country. For example, those born in Brazil, Canada, India and Mexico (along with several others) are not currently eligible for the lottery program as their application period expired in 2007. However, if the number of immigrants from these countries is reduced in proportion to the rest of the world in the next few years, they may again become eligible for the lottery program.
You can also meet the residency requirement if your spouse was born in an eligible country, assuming that your spouse also receives a visa and enter the U.S. with you.
Eligible recipients must also meet an employability requirement: you must either have a high school diploma (or equivalent) or at least two years’ experience in a skilled profession.
For more on the Visa Lottery program, read the book Immigration Made Simple.