The Immigration and Nationality Act of 1965 (H.R. 2580; Pub.L. 89–236, 79 Stat. 911, 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 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.
This summary is from Wikipedia.