Chapter 1 - Purpose and Background
Certain noncitizens may not be allowed to enter or obtain status in the United States because they are inadmissible. These noncitizens may overcome the inadmissibility if they are eligible to apply for and receive a waiver.
USCIS, in its administration of waiver laws and policies, seeks to:
Promote family unity and provide humanitarian results;
Provide relief to refugees, asylees, victims of human trafficking  and certain criminal acts,  and other humanitarian and public interest applicants who seek protection or permanent residency in the United States;
Advance the national interest by allowing noncitizens to be admitted to the United States if such admission could benefit the welfare of the country;
Ensure public health and safety concerns are met by requiring that applicants satisfy all medical requirements prior to admission or, if admitted, seek any necessary treatment; and
Weigh public safety and national security concerns against the social and humanitarian benefits of granting admission to a noncitizen.
Considerations of family unity, humanitarian concerns, public and national interest, and national security may differ depending on the specific waiver an applicant is seeking.
With the enactment of the Immigration and Nationality Act of 1952 (INA),  Congress established a variety of inadmissibility grounds to protect the interests of the United States. Congress considered waivers as a special remedy to the grounds of inadmissibility. 
Congress later amended the INA in 1957, easing many stricter provisions of the earlier legislation.  For example, it allowed certain noncitizen relatives of U.S. citizens or lawful permanent residents (LPR) to apply for and obtain a waiver of certain grounds of exclusion or deportation (now inadmissibility or removal). 
When passing the 1957 amendments, Congress created exceptions to many strict provisions from the 1952 Act to promote family unity. For Congress, in many circumstances, it was more important to keep families together than to stringently enforce inadmissibility grounds. 
Congress tightened waiver requirements and availability once again with the Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA).  For example, IIRIRA made waivers of criminal inadmissibility  unavailable to LPRs who were convicted of an aggravated felony or who had not continuously resided in the United States for at least 7 years before initiation of removal proceedings.
IIRIRA also created new inadmissibility grounds, such as the ground of inadmissibility on account of unlawful presence, and corresponding waivers.
[^ 4] See INS v. Errico, 385 U.S. 214, 218 (1966), citing H.R. 1365, 82nd Cong. 128 (1952).
[^ 5] See Act of September 11, 1957, Pub. L. 85-316 (September 11, 1957).
[^ 6] The INA gives the Attorney General and the Secretary of Homeland Security statutory authority to grant waivers. Some sections of the INA, however, still refer exclusively to the “Attorney General.” Under the Homeland Security Act of 2002, Pub. L. 107–296 (PDF) (November 25, 2002), the authority to grant waivers was also given to the Secretary of Homeland Security.
[^ 7] See INS v. Errico, 385 U.S. 214, 219-20 (1966), citing H.R. 1199, 85th Cong. 7 (1957).