Immigration law provides an avenue of relief from some grounds of inadmissibility in the immigrant visa and adjustment of status contexts. For example, there are waivers for health-related grounds, fraudulent misrepresentation, criminal grounds, lack of vaccines, and unlawful presence. Most waivers require you to prove extreme hardship to a qualifying relative, which is hardship that exceeds the usual or expected and must go beyond what is typically associated with deportation. The qualifying relative differs depending on the waiver.
If you are coming to the U.S. permanently seeking a green card and you have been told you are inadmissible or think you are, you can file a waiver of this inadmissibly on Forms I-602, I-601 or I-601A. Most waivers are filed on Form I-601 except for waivers of unlawful presence for those who are currently in the U.S. with qualifying relatives or refugees, which are on I-602s. Only after a waiver is approved will you qualify for the visa you are applying for. If you must file an I-601 waiver, sometimes you must file this after you are outside the U.S. after a determination of inadmissibility.
If you are in the U.S. and your only inadmissibility is unlawful presence, you may be able to file the I-601A, provisional unlawful presence waiver, in the U.S. This allows you to wait for a decision on your application before traveling outside the U.S. to process your visa at an embassy or consulate. Before 2013, you were required to remain outside the U.S. while an unlawfully presence waiver was being adjudicated. Applicants for provisional waivers were required to demonstrate extreme hardship to either a U.S. citizen spouse or parent (a more limited group of qualifying relatives). In 2016, the provisional waiver was expanded to include anyone who would be eligible to apply for a waiver, including applicants coming through employment-based immigration, the diversity lottery, immigrant-based immigration, or any other immigrant classification.