The United States on Monday lifted a travel ban that had been in place for nearly two years, reopening borders for vaccinated travelers from 33 countries. Airports and land-border checkpoints were the scenes of jubilant reunions. Airlines are bracing for an influx of travelers in the coming weeks and months, including binational couples and families who had been separated.

Here’s what to know about the changes in the U.S. international travel policy.

Who did the ban affect?

The reopening applies to 33 previously banned countries, including most of the European Union, the United Kingdom, India, China, Iran, Brazil and South Africa. Travelers must be fully vaccinated and provide results of a negative coronavirus test or documentation proving recovery from covid-19.

Land borders with Canada and Mexico were only open for “essential” travel, but the restriction has also dropped.

What are the vaccine and testing requirements?

Testing is required to enter the United States by air, regardless of vaccination status. Those traveling by land border are not required to provide a negative coronavirus test.

Foreign nationals must be fully vaccinated and show proof of a negative rapid or PCR coronavirus test within three days of boarding their flight to the United States. “Self-tests” can be used if they meet U.S. testing requirements, including real-time supervision from a telehealth service.

“Fully vaccinated” is defined as 14 days after a shot of an approved single-dose vaccine (such as Johnson & Johnson), or 14 days after your second shot of an approved 2-dose series vaccine (e.g., Pfizer-BioNTech and Moderna) or a mix-and-match combination. Limited exceptions apply to the vaccination and testing requirements for people from countries with little access to vaccines who are facing medical emergencies, are armed forces members or immediate family, or are diplomats and ship and airline crews, among others.

According to the U.S. State Department, falsifying any vaccine or testing information could result in criminal penalties and fines.

Can unvaccinated kids enter?

Yes. But kids between ages 2 and 17 need to take a coronavirus test before they travel. According to the State Department, kids under 18 do not have to meet the vaccine requirement, “given both the ineligibility of some younger children for vaccination, as well as the global variability in access to vaccination for older children who are eligible to be vaccinated.”

Unvaccinated kids who are traveling with a fully vaccinated adult can show proof of a negative test taken within three days of departure. If kids are traveling with unvaccinated adults, they need to show proof of a test taken within one day of departure. Children under 2 do not need to take a test, but the Centers for Disease Control and Prevention recommends testing for that group “whenever possible,” the State Department says.

Are all vaccines allowed?

No. Acceptable vaccines must be authorized by the Food and Drug Administration or listed for emergency use by the World Health Organization. That includes the one-dose Johnson & Johnson vaccine and several two-dose options, including Pfizer-BioNTech, Moderna, AstraZeneca, Covaxin, Covishield, Sinopharm and Sinovac.

While the CDC has not recommended using different types of shots when people are getting their initial course of vaccination, the agency said it will allow international travelers who have mixed and matched. The practice is used in countries outside the United States.

How do visitors show proof of vaccination?

The State Department says proof of vaccination should be a paper or digital record — such as an app — that is issued by an official source. It needs to include the name of the traveler, their date of birth, the type of vaccine and the dates that all doses were administered.

Airlines will be in charge of verifying travelers’ status. They will match the name and birth date on the record to confirm the passenger’s identity, make sure the vaccination record was issued by an official source, and review the type of vaccine, dates, number of doses and other information to make sure the traveler qualifies as “fully vaccinated.”

What about Mexico and Canada?

Land borders with Canada and Mexico are now reopened to fully vaccinated foreign travelers. Those traveling by land don’t need a negative coronavirus test to enter the United States. Children are also exempt from the vaccination requirement.