In honor of Roll Call’s upcoming 50th anniversary, we present the first in a series of top 10 lists that assess Congress’ achievements, embarrassments and curiosities since 1955.

Over the past 50 years, Congress has passed approximately 28,000 bills. But only a small minority of them have had a profound impact on American life.

In an attempt to single out the 10 most important pieces of legislation during the past half-century, we looked for those that most significantly shaped the nation’s future course, whether for better or for worse. Domestic and foreign policy were both fair game, and we didn’t quibble about whether the measure was a bill, a resolution or a treaty ratification. (We did exclude confirmations of appointees, however.) Also, we valued diversity in subject matter so the list wouldn’t overflow with bills on the same general topic.

To gather ideas, we consulted a blue-ribbon panel of Congressional scholars: Joel Aberbach of the University of California at Los Angeles, Scott Adler of the University of Colorado, David Boaz of the Cato Institute, David Brady and Morris Fiorina of the Hoover Institution, Lee Edwards of the Heritage Foundation, Allan Lichtman of American University, Burdett Loomis of the University of Kansas, David Mayhew of Yale University, Bert Rockman of Ohio State University, Steven Smith of Washington University, Rick Striner of Washington College, James Thurber of American University and Eric Uslaner of the University of Maryland.

After sifting through these scholars’ nominations, we settled on a top 10. We also added a few near-misses.

As it happened, the scholars, though they worked independently of each other, reached a clear consensus on the top 5 pieces of legislation. Beyond that, they diverged wildly — so for the rest of the measures on our list, we applied our own judgment.

Though it wasn’t our intention, the top 10 and the runners-up together contain at least one measure signed by every president since 1955 except for Gerald Ford. There’s also a virtually equal divide between measures signed by Republican and Democratic presidents. Here’s the list:

1. Civil Rights Act (1964). Virtually every scholar, liberal and conservative, ranked this act first on their list. Its impact is unquestionable: Coming after a decade of civil rights struggle in the South and on the heels of President John F. Kennedy’s assassination, the hotly contested act effectively ended racial discrimination in public accommodations and employment. Less noticed initially, but arguably just as significant, is the act’s role in ending discrimination based on sex. “America could scarcely lay claim to be a moral exemplar for the world prior to this act,” Lichtman said.

2. Voting Rights Act (1965). A few of our scholars ranked this act equal to, or even higher than, the Civil Rights Act. They cited not only its intended impact on ensuring the vote for blacks, but also its unintended but profound role in realigning American politics. After the VRA, white voters, first in the South and then elsewhere, flocked to the Republican Party. This in turn made possible America’s turn to the right on economic, social and foreign policy since the 1980s.

3. Medicare and Medicaid acts (1965). Together, these programs have protected the health of countless elderly and poor Americans, putting it “right up there with Social Security in its impact on American life,” in Aberbach’s words. And looking into the future, the programs are so enormous that both the federal government and state governments are destined to face intractable budget challenges.

4. Federal-Aid Highway Act (1956). Its title is obscure, but its impact is not: The act created the Interstate Highway System, which touched virtually every aspect of American life in the past 50 years. Faster roads intensified economic growth, boosted domestic tourism and made possible just-in-time manufacturing processes. Interstates also produced suburbanization, which dramatically changed lifestyles (more space, but longer commutes), drove downtowns into decline and led to the development of previously empty land. Population shifted to the Sun Belt, changing the nation’s political balance. And the Interstates irreversibly solidified the primacy of the automobile, worsening air pollution and climate change and cementing the strategic importance of the Middle East.

5. Economic Recovery Tax Act (1981). ERTA, the keystone of President Ronald Reagan’s economic program, cut individual taxes by 25 percent, indexed tax rates to end “bracket creep” and made other technical changes that have had an enormous influence on the economy in the past quarter-century. In a larger sense, ERTA ushered in an era in which big government, and sometimes any government, ceased to be seen as an unalloyed good. The act “changed the direction of the federal government — the biggest shift since the New Deal — and laid the foundation for Republican success,” Uslaner said.

6. National Defense Education Act (1958). Passed in response to the Soviet launch of the satellite Sputnik, NDEA provided $575 million for education and low-interest loans for students. Its stated focus on boosting achievement in science and mathematics helped enhance the nation’s intellectual capital, laying the groundwork for decades of American innovation in science and technology and, in turn, providing a basis for economic growth, military superiority and world leadership. The act is relatively forgotten today; only two of our panelists cited it.

7. Tonkin Gulf Resolution (1964). The Tonkin Gulf Resolution authorized military action in Vietnam, leading the United States into a conflict that left more than 50,000 Americans dead and bequeathed tremendous divisiveness at home. Beyond that, however, the resolution — which was based on an attack that may not have taken place at all — was a major landmark for presidential authority on waging war. Ever since, presidents have exercised largely unfettered power to commit American troops abroad, with little say by Congress, despite passage of the War Powers Resolution of 1973.

8. Amendments to Immigration and Nationality Act (1965). This legislation, sponsored by Sen. Phil Hart (D-Mich.) and Rep. Emanuel Celler (D-N.Y.), is the sleeper of the list. It removed national-origins quotas for immigrants that had stood since 1921, thus clearing the way for a new wave of mass immigration that transformed America. To supporters, these immigrants have strengthened America’s economy; to detractors, they have been a burden, especially for native-born Americans who face new competition for jobs. Either way, the influx of immigrants from around the globe has irrevocably redefined American culture. “At the time, it wasn’t thought to be all that important, and it wasn’t very controversial,” Mayhew said. “But few acts of Congress have ever been as consequential.”

9. Clean Air Act Amendments (1970). Other landmarks of environmental legislation could easily have filled this spot — such as the National Environmental Policy Act, passed the previous year — but this measure attracted the most support among our panelists. It played a key role in the federal government’s pre-emption of state regulatory authority over the environment, and, coming shortly after the first Earth Day, it was designed to be a clear signal that environmental regulation and economic growth were not incompatible. Despite some ups and downs, that view still holds considerable sway.

10. Personal Responsibility and Work Opportunity Reconciliation Act (1996). This major overhaul of welfare, requiring work rather than government assistance, directly affected many Americans. But it was also passed by a Republican Congress and signed by a Democratic president, Bill Clinton, thus signaling the bipartisan abandonment — albeit a long time coming — of the ideas that undergirded President Lyndon Johnson’s Great Society.

Seven additional measures came very close to making the top 10. The runners-up:

• End of the military draft (1973). This one, among these measures, was a case of Congress allowing a law to expire, rather than passing something. The elimination of the draft not only began to heal perhaps the most controversial aspect of the Vietnam War, but it led directly to the creation of an all-volunteer military, which, barring an unprecedented military threat, is likely to continue into the foreseeable future.

• Gun Free School Zones Act (1990). Another oddity: This law’s significance comes not from its passage, but from its being declared unconstitutional. In United States v. Lopez (1995), the Supreme Court threw out the law as an unconstitutional exercise of power under the constitution’s Commerce Clause, thus curbing the long-exercised federal power to regulate interstate commerce. This precedent has shaped legislation and jurisprudence ever since.

• Trade Expansion Act (1962). This act set the United States firmly on the path of free trade, producing both great economic expansion and dislocation.

• Nuclear Test Ban Treaty ratification (1963). This treaty prohibited nuclear weapons tests in the atmosphere, outer space and under water. It not only curbed the spread of dangerous radioactivity in the environment, but it also set a precedent for future international accords that, in all likelihood, prevented the outbreak of nuclear war. Even as other international treaties have cracked under the strain of national interest, this one has remained rock-solid for more than four decades.

• U.S. Airline Deregulation Act (1978). The deregulation of the airlines — approved by a Democratic Congress and President Jimmy Carter — was subsequently used, primarily by Republicans, as a model for the deregulation of other sectors, including telecommunications and financial services. It became a milestone in the building of popular confidence in the private sector and dissatisfaction with government regulation.

• Comprehensive Drug Abuse Prevention and Control Act (1970). This act consolidated previous drug laws and strengthened law enforcement by allowing police to conduct “no-knock” searches. It was probably the key law in the escalation of the war on drugs — a war that remains with us 35 years later, without an end in sight.

• Amendments to the Social Security Act (1972). This act increased Social Security payments and indexed them to inflation. “It virtually wiped out homelessness among the elderly,” Mayhew said.

One additional contender earns a grade of “incomplete”:

• PATRIOT Act (2001). Depending on who one listens to, this law, passed in the wake of the Sept. 11, 2001, terrorist attacks, could have either a major positive impact on law enforcement or a major negative impact on civil liberties. The law is too new to know who’s right — and, equally important, the act could be whittled back when it comes up for reauthorization this year.

And how were these laws seen at the time of their passage? In all, there is a modest, but not universal, correlation between the intensity of contemporary media coverage and an act’s eventual significance.

Frank Baumgartner of Pennsylvania State University and Bryan Jones and John Wilkerson of the University of Washington measured the amount of coverage afforded by Congressional Quarterly. Several of the measures on Roll Call’s list — including each of the top three — rank among CQ’s most-written-about bills since 1955. But most on our list do not.