The last comprehensive legalization program had a filing deadline of sunset on April 30, 2001. In general, section 245(i) of the Immigration and Nationality Act allowed an otherwise admissible alien who has an immediately available immigrant visa to apply for adjustment of status upon payment of a $1,000 surcharge, even though the alien entered the United States without inspection in violation of section 245(a) or is barred by section 245(c) of the Act. While this program entered many years ago, many people may still be able to benefit through the concept of grandfathering. Grandfathering 245(i) is available to a person (and possibly his immediate family members) if an immigrant petition or labor certification was filed before the deadline of 245(i) for that foreign national and was "approvable when filed." If this is the case, then the foreign national can adjust status, that is obtain permanent residency a.k.a. a greencard through a subsequent petition.
For further relevant guidance, see below: