Recently, a client who is a US citizen contacted me about sponsoring her elderly parents for legal permanent residency and the optimum way to proceed. US citizens may sponsor their spouse, children, parents and siblings for legal permanent residency.
Foreign nationals can obtain legal permanent residency either by adjusting (changing) their status in the US or by going to a US Consulate abroad and getting the immigrant visa. For adjustment, the I-130 and the I-485 are the primary forms. If the adjustment application is based on marriage, then the foreign national and his or her spouse will be interviewed to determine if it is a real marriage and the foreign national is eligible (for parents of US citizens this interview is usually waived). The foreign national will definitely be scheduled for biometrics around one month after filing. Also, with the adjustment application the foreign national can file for the advance parole travel permission, which allows him or her to travel abroad while the I-485 is pending. If the foreign national departs the US before obtaining the advance parole document, then he or she will abandon the I-485 and need to consular process abroad for the immigrant visa (although there are exceptions for H-1Bs and L1s).
The one very important caveat is that foreign nationals cannot enter the US as a nonimmigrant with the intent to file to adjust their status in the US (with the exception of dual intent nonimmigrants such as H-1Bs and L-1s). They can enter as nonimmigrants, such as B-2 visitors or F-1 students, and then have an I-130 filed for them to obtain their immigrant visas abroad. Also, if the petitioner files only the I-130 immigrant visa petition for consular processing abroad, then the foreign national may not be able to enter as a nonimmigrant while the case is pending (except for those with dual intent visas like the H-1B or L-1).
If the foreign national does enter as a nonimmigrant (without a dual intent visa) with the “illegal” intent to obtain legal permanent residency in the US through adjustment of status, then the US government could make a fraud finding against this individual and bar the individual from entering the US. There is a waiver available for a foreign national who can show extreme hardship to a US citizen or legal permanent resident spouse or parent, but these cases are very challenging.