Generally, the US Immigration Service permits the immigration through a family member, the immigration through an employment, the immigration through an investment, the immigration as an asylum or a refugee and the immigration through an international adoption. However, there are some specific cases for a person to apply to the US Immigration Service, such as the immigration for eligible individuals from Vietnam, Cambodia, Laos or Violence Against Women Act (VAWA), the immigration through the Legal Immigration Family Equity Act (LIFE), the immigration through the Cuban Adjustment Act, the immigration through the Haitian Refugee Immigration Fairness Act of 1998 (HRIFA) and some others. In any case, a prospective immigrant must obtain an immigrant visa number, which is based on the preference category in which he falls.
Once you send your visa petition to the USCIS (US Citizenship and Immigration Services), it will be approved or denied. The USCIS will notify you if the visa petition is approved. The USCIS will send the approved visa petition to the Department of State's National Visa Center, where it will remain until an immigrant visa number is available. Only after that, if you are already in the United States, you may apply to adjust to a permanent resident status. If you are outside the United States, you will be notified to go to the local US consulate to complete the processing for an immigrant visa.
Each category or immigration suggests its specific requirements to your eligibility, about which it is better to consult at the Immigration Advisory Service. For instance, the US Immigration Service permits the immigration through an employment for priority workers (such as outstanding professionals or researchers, foreign nationals of extraordinary ability in the sciences, arts, etc), professionals with advanced degrees or exceptional abilities, skilled or professional workers and special immigrants (foreign national religious workers, employees and former employees of the U.S. Government abroad).
One more way to receive a cherished Green Card is to participate in the Diversity Lottery Program, which makes fifty five thousand immigrant visas available through a lottery to people from the countries with low rates of immigration to the United States. The State Department (DOS) holds the lottery every year and randomly selects approximately one hundred and ten thousand applicants from all qualified entries. If you receive a visa through the Diversity Visa Lottery Program, there is no need to file an application to the US Immigration Service and you will be authorized to live and work permanently in the United States.
A benefit of the Diversity Lottery Program is that you will also be allowed to bring your spouse and any unmarried children under the age of twenty one to the United States. However, these visas are not available for people, who come from countries that have sent more than fifty thousand immigrants to the United States in the past five years; hence, you should check whether your country is eligible to participate in the lottery. You may also be eligible to apply if your parent was born in a country that is eligible to participate. Commonly, the information is available at your local Immigration Service and the State Department publishes the names of countries that are eligible to participate before each year's lottery.