Many immigrants to the US work hard in the US and contribute to the US economy. As an acknowledgement, the US government has made it possible for people to apply for an immigrant visa and permanent residency through employment. That is, someone who works hard in the US eventually may have the option of applying for a green card and living and working permanently in the US. If you are a worker in the US on a valid visa and are eligible to get a green card through employment, you can apply for permanent residency by filing I-140 (Immigrant Petition for Alien Worker).