The Immigration and Nationality Act of 1965 (H.R. 2580;, 79 Stat., enacted June 30, 1968), also known as the Hart–Celler Act,  changed the way quotas were allocated by ending the National Origins Formula that had been in place in the United States since the Emergency Quota Act of 1921. Representative Emanuel Celler of New York proposed the bill, Senator Philip Hart of Michigan co-sponsored it, and Senator Ted Kennedy of Massachusetts helped to promote it.
The Hart–Celler Act abolished the quota system based on national origins that had been American immigration policy since the 1920s. The 1965 Act marked a change from past U.S. policy which had discriminated against non-northern Europeans. In removing racial and national barriers the Act would significantly, and unintentionally, alter the demographic mix in the U.S. 
The new law maintained the per-country limits, but also created preference visa categories that focused on immigrants' skills and family relationships with citizens or U.S. residents. The bill set numerical restrictions on visas at 170,000 per year, with a per-country-of-origin quota. However, immediate relatives of U.S. citizens and "special immigrants" had no restrictions. 
The Hart–Celler Act of 1965 marked a radical break from the immigration policies of the past. Previous laws restricted immigration from Asia and Africa, and gave preference to northern and western Europeans over southern and eastern Europeans.  In the 1960s, the United States faced both foreign and domestic pressures to change its nation-based formula, which was regarded as a system that discriminated based on an individual's place of birth. Abroad, former military allies and new independent nations aimed to delegitimize discriminatory immigration, naturalization and regulations through international organizations like the United Nations.  In the United States, the national-based formula had been under scrutiny for a number of years. In 1952, President Truman had directed the Commission on Immigration and Naturalization to conduct an investigation and produce a report on the current immigration regulations. The report, Whom We Shall Welcome, served as the blueprint for the Hart–Celler Act.  At the height of the Civil Rights Movement the restrictive immigration laws were seen as an embarrassment. President Lyndon Johnson signed the 1965 act into law at the foot of the Statue of Liberty.
The immigration into the country of "sexual deviants", including homosexuals, was still prohibited under the legislation. The INS continued to deny entry to homosexual prospective immigrants on the grounds that they were "mentally defective", or had a "constitutional psychopathic inferiority" until the Immigration Act of 1990 rescinded the provision discriminating against gay people. 
The Hart–Celler Act amended the Immigration and Nationality Act of 1952 (McCarran-Walter Act), while it upheld many provisions of the Immigration Act of 1924. It maintained per-country limits, which had been a feature of U.S. immigration policy since the 1920s, and it developed preference categories.
- One of the main components aimed to abolish the national-origins quota. This meant that it eliminated national origin, race, and ancestry as basis for immigration.
- It created a seven-category preference system, which gave priority to relatives of U.S. citizens and legal permanent residents and to professionals and other individuals with specialized skills.
- Immediate relatives and "special immigrants" were not subject to numerical restrictions. Some of the "special immigrants" include ministers, former employees of the U.S. government, foreign medical graduates, among others.
- For the first time, immigration from the Western Hemisphere was limited.
- It added a labor certification requirement, which dictated that the Secretary of Labor needed to certify labor shortages.
- Refugees were given the seventh and last category preference with the possibility of adjusting their status. However, refugees could enter the United States through other means as well like those seeking temporary asylum.
Wages under Foreign Certification
As per the rules under the Immigration and Nationality Act (INA), U.S. organizations are permitted to employ foreign workers either temporarily or permanently to fulfill certain types of job requirement. The Employment and Training Administration (ETA) under the U.S. Department of Labor (DOL) is the body that usually provides certification to employers allowing them to hire foreign workers in order to bridge qualified and skilled labor gaps in certain business areas. Employers must confirm that they are unable to hire American workers willing to perform the job for wages paid by employers for the same occupation in the intended area of employment. However, some unique rules are applied to each category of visas. They are as follows:
- H-1B and H-1B1 Specialty (Professional) Workers should have a pay, as per the prevailing wage – an average wage that is paid to a person employed in the same occupation in the area of employment; or that the employer pays its workers the actual wage paid to people having similar skills and qualifications.
- H-2A Agricultural Workers should have the highest pay in accordance to the (a) Adverse Effect Wage Rate (AEWR), (b) the present rate for a particular crop or area, or (c) the state or federal minimum wage. The law also stipulates requirements like employer-sponsored meals and transportation of the employees as well as restrictions on deducting from the workers' wages.
- H-2B Non-agricultural Workers should receive a pay that is in accordance with the prevailing wage (mean wage paid to a worker employed in a similar occupation in the concerned area of employment).
- D-1 Crewmembers (longshore work) should be paid the current wage (mean wage paid to a person employed in a similar occupation in the respective area of employment).
- Permanent Employment of Aliens should be employed after the employer has agreed to provide and pay as per the prevailing wage trends and that it should be decided on the basis of one of the many alternatives provisioned under the said Act. This rule has to be followed the moment the Alien has been granted with permanent residency or the Alien has been admitted in the United States so as to take the required position. 
The Hart–Celler Act was widely supported in Congress. Senator Philip A. Hart introduced the administration-backed immigration bill which was reported to the Senate Judiciary Committee's Immigration and Naturalization Subcommittee.  Representative Emanuel Celler introduced the bill in the House of Representatives, which voted 320 to 70 in favor of the act, while the Senate passed the bill by a vote of 76 to 18.  In the Senate, 52 Democrats voted yes, 14 no, and 1 abstained. Among Senate Republicans, 24 voted yes, 3 voted no, and 1 abstained.  In the House, 202 Democrats voted yes, 60 voted no and 12 abstained, 118 Republicans voted yes, 10 voted no and 11 abstained.  In total, 74% of Democrats and 85% of Republicans voted for passage of this bill. Most of the no votes were from the American South, which was then still strongly Democratic. During debate on the Senate floor, Senator Kennedy, speaking of the effects of the act, said, "our cities will not be flooded with a million immigrants annually. ... Secondly, the ethnic mix of this country will not be upset". 
Michael A. Feighan and other conservative Democrats had insisted that "family unification" should take priority over "employability", on the premise that such a weighting would maintain the existing ethnic profile of the country. That change in policy instead resulted in chain migration dominating the subsequent patterns of immigration to the United States and consequently a more ethnically diverse population.  
On October 3, 1965, President Lyndon B. Johnson signed the legislation into law, saying, "This [old] system violates the basic principle of American democracy, the principle that values and rewards each man on the basis of his merit as a man. It has been un-American in the highest sense, because it has been untrue to the faith that brought thousands to these shores even before we were a country". 
The proponents of the Hart–Celler Act argued that it would not significantly influence United States culture. President Johnson called the bill "not a revolutionary bill. It does not affect the lives of millions."  Secretary of State Dean Rusk and other politicians, including Senator Ted Kennedy, asserted that the bill would not affect US demographic mix.  However, the ethnic composition of immigrants changed following the passage of the law. Specifically, the Hart–Celler Act allowed increased numbers of people to migrate to the United States from Latin America, Asia, Africa, and the Middle East.
Prior to 1965, the demographics of immigration stood as mostly Europeans; 68 percent of legal immigrants in the 1950s came from Europe and Canada. However, in the years 1971–1991, immigrants from Hispanic and Latin American countries made 47.9 percent of immigrants (with Mexico accounting for 23.7 percent) and immigrants from Asia 35.2 percent. Not only did it change the ethnic makeup of immigration, but it also greatly increased the number of immigrants—immigration constituted 11 percent of the total U.S. population growth between 1960 and 1970, growing to 33 percent from 1970–80, and to 39 percent from 1980–90. The elimination of the National Origins Formula and the introduction of numeric limits on immigration from the Western Hemisphere, along with the strong demand for immigrant workers by U.S. employers, led to rising numbers of unauthorized immigrants in the U.S. in the decades after 1965, especially in the Southwest.  Policies in the Immigration Reform and Control Act of 1986 that were designed to curtail migration across the Mexican-U.S. border led many unauthorized workers to settle permanently in the U.S.  These demographic trends became a central part of anti-immigrant activism from the 1980s leading to greater border militarization, rising apprehension of migrants by the Border Patrol, and a focus in the media on the supposed criminality of immigrants.
In January 2017, president Donald Trump's Executive Order 13769 temporarily halting immigration from 7 majority-Muslim nations made reference to the Immigration and Nationality Act of 1952; however, federal courts ruled the Executive Order violated the prohibitions on discrimination by nationality and religion in the 1965 Act. In June, the US Supreme Court overrode both appeals courts and allowed the second ban to go into effect, but carved out an exemption for persons with “bona fide relationships” in the US.