In June, the European Union officially recommended its member countries reopen their borders to American tourists after more than a year of tight restrictions. The United Kingdom has also placed the United States on an “amber” list, which means American travelers are allowed in, but must quarantine for 10 days and show proof of a negative coronavirus test.

But residents of Europe’s Schengen area — spanning 29 countries, city-states and micro-states — as well as those in the United Kingdom and the Republic of Ireland are still barred from traveling to the United States, unless they are a U.S. citizen or they spend 14 days before arrival in a country that is not on the Centers for Disease Control and Prevention’s prohibited list. Certain family members are also exempt.

The restrictions were first put in place in March 2020. Although President Donald J. Trump briefly ordered an end to the ban on European travelers during his last week in office, President Biden quickly rescinded the move.

Discussions about when to resume inbound travel have been opaque. In late June, Secretary of State Antony Blinken said it was too soon to say when the United States would lift travel curbs for European Union citizens.

“We are anxious to be able to restore travel as fully and as quickly as possible. We’re very much guided by the science, by our medical experts. That has to be the foundational principle on which we’re looking at this,” Mr. Blinken said at a news conference in Paris, adding that he “can’t put a date on it.”

Transportation Secretary Pete Buttigieg said on July 8 that the United States was not yet ready to lift restrictions on international travel.

“A lot of this is based on what’s going on with progress on the vaccines,” Mr. Buttigieg said in an interview with Bloomberg TV. “Obviously we see good news and bad news out there in terms of the variants. One moment, you’re reading about a variant happening across the world, the next you know, it’s becoming the dominant strain here in the U.S.”

Here’s what we know about the United States’ border closures with European countries.

In June, the White House announced the creation of “working groups” with the European Union, the U.K., Canada and Mexico to reopen borders.

“While these groups have met a number of times, there are further discussions to be had before we can announce any next steps on travel reopening with any country,” Kevin Munoz, a White House spokesman, said in a statement. “We have made tremendous progress domestically in our vaccination efforts, as have many of these other countries, but we want to ensure that we move deliberately and are in a position to sustainably reopen international travel when it is safe to do so.”

During the first meeting of the E.U.-U.S. working group, which took place on June 18, officials said they would continue discussions about how to safely reopen travel between the two regions.

“Reciprocity is an important part of our approach to lifting restrictions on non-E.U. countries,” Adalbert Jahnz, a spokesman for the European Commission, said in a statement. He added that the E.U. has “received reassurances that this is a high priority issue for the U.S. administration.”

The Biden administration has repeatedly said that it would rely on the science to guide its decision to relax border restrictions. But the picture of the virus has improved in many parts of the United States and in Europe, and the White House has not announced specific benchmarks for reopening.

Ned Price, the State Department spokesman, said last month that U.S. officials were monitoring the development of the virus, including the spread of worrisome variants.

“I’m not able to put a specific time frame on it only because it will depend in large part on the course of the epidemiology,” Mr. Price said at a press briefing on June 21.

Even though reported coronavirus cases in the United States have dropped from record-high peaks in the winter, public health experts have raised concerns about the spread of the highly contagious Delta variant, which the C.D.C. estimates is now the dominant variant in the United States. The country is reporting an average of about 15,259 new cases a day, according to a New York Times database.

After a slow start, vaccination campaigns have started to pick up. The European Union, initially beset with disruptions in supplies of the AstraZeneca and Johnson & Johnson Covid-19 vaccines, pivoted in April to rely heavily on the Pfizer-BioNTech vaccine. Reported coronavirus cases also remain at low levels in many parts of Europe as more people get vaccinated, but the spread of variants has fueled some outbreaks.

The United Kingdom has seen a sharp rise in reported cases since dealing with an outbreak of the Delta variant, but it has not yet been followed by a surge in hospitalizations or deaths. Prime Minister Boris Johnson recently announced that the country would lift most remaining restrictions on July 19.

In Portugal, officials in early July announced new curfews in Lisbon, Porto and other popular tourism spots, reversing course after it had reopened its economy to prepare for summer visitors.

Travel lobbying groups and airlines have urged the United States to reopen travel with Europe to bolster the economy. On July 7, a coalition of 24 trade organizations released a blueprint for reopening borders safely, calling for the United States to allow in fully vaccinated travelers from regions that have high vaccination rates and low levels of variants of concern.

“We know international travel can be restarted and particularly with countries that have similar vaccination rates to the U.S.,” Roger Dow, the chief executive of the U.S. Travel Association, said at a webinar on July 7. He specifically called for the United States to immediately reopen travel with the U.K., pointing out that the country has fully vaccinated about 51 percent of its population.

Some public health experts have also called for the reopening of international travel for vaccinated people.

Barry Bloom, a research professor and former dean of the Harvard T.H. Chan School of Public Health, said that United States officials may be wary of the spread of more contagious variants, but that the presence of the Delta variant was already evident in the country.

“Keeping the Brits out is not going to change that fact,” Dr. Bloom said.

The C.D.C.’s list of countries from which travel is prohibited also includes China, Iran, Brazil, South Africa and India.