If you are from another country and would like to come to the United States to live permanently, there may be multiple ways to achieve that goal. The possible routes to becoming a permanent lawful resident include employment based and family-based immigration. Depending on the type of visa sought, the approach taken will vary.
Where employment-based immigration is concerned, here too there are several ways to proceed. Under one of those options, when a worker has a certain set of skills, an employer can sponsor you. Depending on the category one qualifies for, to secure a visa based on employment, either you or your sponsoring employer has to file an I-140 Petition for Alien Worker with U.S. Citizenship and Immigration Services.
To immigrate via the family based system, another family member who is already a U.S. citizen can file a petition for certain family members including a spouse, children, parent or sibling. A family member need not be a citizen to file a petition to bring a family member to the U.S. In other cases someone who has a green card can take the same approach with a spouse or a child who is not married.
There are requirements that someone seeking a visa under any visa process needs to meet. In addition to applications and fees, supporting documents need to be provided at specific times. Because the average person is not familiar with these requirements, it is usually a good idea to work with an immigration lawyer in these matters.
Source: U.S. Department of State, “The Immigrant Visa Process,” Accessed Oct. 29, 2014