U.S. immigration law lists dozens of reasons why a person could be ineligible for permanent resident status. Some of these reasons can be forgiven through a process known as a waiver application. Applications for waivers are complicated and approval depends on factors that may not seem obvious. 

A common waiver is called an "unlawful presence" waiver. This is needed if a person enters the United States without inspection and then wishes to depart the United States to finish processing for an immigrant visa with a U.S. consulate. Other waivers are available for minor crimes, misrepresentations, and other reasons. Those who are in the United States and believe they may need any type of waiver should consult with an immigration attorney experienced with waiver applications.