The most difficult way to get a green card, or permanent residency, is to obtain a Diversity Visa, otherwise known as the Green Card Lottery. Each year, the U.S. gives out 55,000 green cards to applicants who reside in low admission countries – those that have had fewer than 50,000 people who have immigrated to the U.S. in the last five years.
Anyone who lives in one of the eligible countries can apply for the green card lottery, even if the person is living in the United States, legally or illegally. Applicants need only provide an address where he or she can be notified, even if it is a U.S. address and you are an illegal immigrant (you do not have to provide your home address, just an address where you can be notified).
Moreover, winners of the green card lottery can also bring in their immediate family members as permanent residents, so long as you live with the spouse or child at the time you win the lottery.
To win the green card lottery, in addition to being a native of one of the eligible countries, you must also have a high school education or its equivalent and have at least two years of training or experience.