Adjustment of Status
If you are already in the United States and an immigrant petition is available to you, adjustment of status (Form I-485) lets you become a permanent resident without leaving the country. The process ties together your entire immigration history — entries, statuses, and prior filings — so eligibility review before filing is not a formality; it is the case.
Talk to a lawyer before filing if you have ever been out of status, worked without authorization, or entered without inspection.