An Adjustment of Status is a process where a foreigner (alien) applies for permanent residence (green card) while in US concurrently or after receiving approval of immigration visa.
To be eligible for adjustment of status, an alien must meet the following criteria:
The alien's immigration petition must have been approved. This criterion is only applicable to those who file a family-based immigration petition (Form I-130). However, an alien who is the immediate relative of a U.S. citizen may file an adjustment of status application along with the immigration petition (Form I-130) filed by the U.S. citizen on his or her behalf.
In addition to this, an I-485 adjustment of status application can be filed concurrently with an I-140 employment-based immigration petition (EB-1 andEB-2), if visa numbers are available.
The alien must not have entered the United States illegally. Aliens must have been inspected and lawfully admitted into the U.S. The USCIS considers that you have been "inspected" when you present yourself to an immigration officer at a U.S. port of entry. You are considered admitted when an officer informs you of such and you are allowed to enter the U.S. As a rule, your I-94 and/or the Immigration and Naturalization Stamp in your passport is an indication that you have been admitted legally.
The Alien Must Be Admissible to the US. In other word, the alien must not be in situations which triggers immigration bar according to Immigration Act. Being granted adjustment of status is the same as being admitted to the U.S. for permanent residence. The same inadmissibility grounds in section 212(a) of the Act that can apply at a port of entry can apply to an adjustment applicant.
Immigration Visa Is Immediately Available To The Alien. Petitions are subject to the numerical annual quota for immigrant visas. For these aliens, they may only file their adjustment of status applications once the cut-off dates published monthly by the State Department pass the priority dates of their initial immigration petition or the immigrant visa number for the category is current.