If you are a U.S. citizen and at least 21 years old, you are eligible to petition to bring your parents to live and work permanently in the United States.
If you are a lawful permanent resident, you are not eligible to petition to bring your parents to live and work permanently in the United States. ONLY US citizens are allowed to bring their parents to the United States permanently.
For those who are eligible to bring their parents to the US as a legal immigrant, there is a two-step process. First, USCIS must approve an immigrant visa petition that you file for your parent. Then, if your parent is outside the United States, your parent will be notified to go to the local U.S. consulate to complete the processing for an immigrant visa. If your parent is legally inside the U.S., he or she may apply to adjust his or her status to that of a lawful permanent resident using Form I-485.