The United States federal government operates border preclearance facilities at a number of ports and airports in foreign territory. They are staffed and operated by U.S. Customs and Border Protection (CBP) officers. Travelers pass through U.S. Immigration and Customs, Public Health, and Agriculture inspections before boarding their aircraft, ship, or train. This process is intended to streamline border procedures, reduce congestion at U.S. ports of entry, and facilitate travel between the preclearance location and U.S. airports unequipped to handle international travelers.
Preclearance exists at most major Canadian airports. Arrangements also exist with some airports in Bermuda, The Bahamas, Aruba, Ireland, and the United Arab Emirates. Passengers traveling from a preclearance port arrive in the United States as domestic travelers, but are still subject to reinspection at the discretion of Customs and Border Protection.
Preclearance applies to all passengers on every pre-cleared flight regardless of their nationality or purpose of travel.
This process is intended to streamline border procedures, reduce congestion at ports of entry, and facilitate travel between the preclearance location and some U.S. airports that may not be equipped to otherwise handle international travelers. Many more U.S. airports now have customs facilities than when the preclearance program first started in 1952; LaGuardia Airport and Ronald Reagan Washington National Airport are the two largest U.S. airports without customs facilities for commercial travel.
The United States and other countries that allow preclearance have been accused of also being motivated by the desire to prevent the arrival of asylum seekers, who are otherwise protected under the 1951 Refugee Convention's non-refoulement provisions once they arrive at their destination.
Preclearance is particularly beneficial to those who have an ongoing connection (such as a connecting flight) upon arrival in the U.S., as there is no risk of border delays causing them to miss such a connection. A corresponding drawback, however, is that a delay in preclearance could cause the passenger to miss the outbound flight. Air travelers with further connections have their baggage checked through to their destination; without preclearance, the baggage would have to be collected prior to customs inspection and then rechecked onto the subsequent flight.
Another advantage is that Customs and Border Protection (CBP) officers are able to ultimately exclude inadmissible passengers and prohibited goods before a flight, train journey, or voyage commences. This saves CBP the hassle of dealing with them on U.S. soil, thus helping minimise the risk of any untoward incident happening there. Therefore, when a person is denied entry into the United States, he or she is not allowed to board the US-bound flight and has to merely leave the airport by land transport instead of being put on a return flight (unless the passenger arrived at the preclearance airport from an earlier flight).
Preclearance also provides considerable flexibility to the airlines operating in those routes where such a program is available. For example, major U.S. airlines and their subsidiaries routinely operate many daily flights from locations like Toronto or Nassau to New York City. Thanks to the presence of preclearance facilities in Toronto and Nassau, the airlines can choose to conveniently direct their flights from these locations to land at LaGuardia Airport (which has no border protection facilities) instead of John F. Kennedy International Airport (JFK) or Newark Liberty International Airport (EWR), allowing them to save valuable space at JFK and EWR for their other international arrivals.
Preclearance exists at most major Canadian airports, theoretically enabling more convenient travel from those cities to the United States. The waits at some busy preclearance facilities, notably Toronto Pearson Airport (the busiest U.S. preclearance facility), can often exceed the waiting times of non-precleared flights at the destination and cause significant delays to departure schedules. With the notable exceptions of LaGuardia Airport and Ronald Reagan Washington National Airport, many U.S. airports now have more customs facilities compared to when the preclearance program first started in 1952. Reduced staffing levels by U.S. Customs and Border Protection have been blamed by airport authorities, whose pleas have been answered with deferrals due to domestic priorities. NEXUS and similar programs are now being explored and expanded as a means to try to restore some of the original convenience to the preclearance process.
CBP also sets the hours of operation of its preclearance facilities which are often shorter than the operating hours of the airports, seaports, or railway stations they operate in. Transport providers who want their passengers to take advantage of such a facility will need to time their trips to coincide with the preclearance facilities' operating hours. Carriers may mount flights from preclearance airports to the U.S. outside operating hours, but passengers taking such flights will be processed in the same way as most other international passengers upon the flight's arrival on American soil.
Preclearance facilities exist because of agreements made between the U.S. federal government and the governments of the host countries. Travelers who have passed through the U.S. government checks, but whose flight or ship has not departed, remain in the legal jurisdiction of the host country. U.S. officials may question and search travelers with the passenger's permission, but they do not have powers of arrest (for customs or immigration violations or for the execution of outstanding warrants), but they can deny boarding.
Some countries have laws in place that specifically cover preclearance issues. Since CBP does not have legal powers on foreign soil, passengers can be arrested and detained for offences in the host country only by local authorities. Therefore, if a CBP officer has any security but non-immigration/customs-related concerns about a traveller, the attending CBP officer will need to be refer the matter to local officials. Passengers can choose to abandon their flight and refuse search, and unlike in the United States, officers cannot search them without permission. Most preclearance facilities have a sign explaining so. CBP Officers in the Preclearance Division are not armed on foreign soil. However, it is likely that if the Canadian Parliament approves Bill C-23, CBP officers would be allowed to carry sidearms on duty in Canada if they are working in an environment in which Canada Border Services Agency officers are normally armed.
Informal preclearance arrangements between the United States and Canada began at Malton Airport (now Toronto Pearson International Airport) in 1952, following a request from American Airlines. This was extended and formalized with Canada's passage of the Air Transport Preclearance Act in 1974, the 1999 Preclearance Act, and with the 2001 Canada-U.S. Agreement on Air Transport Preclearance. The preclearance agreement is fully reciprocal, meaning the government of Canada has the option of opening Canadian Preclearance facilities in the United States. On average, however, U.S. international airports offer far fewer flights to Canada compared to the reverse, making this an expensive and inefficient proposition that, as of 2019 , has not been exercised by the Canadian government.
On March 16, 2015, U.S. and Canadian officials signed the ministerial-level Agreement on Land, Rail, Marine, and Air Transport Preclearance Between the Government of the United States of America and the Government of Canada, which foresees significant expansion of the scope of preclearance facilities. For instance, under the new agreement, U.S. CBP officers working at U.S. preclearance facilities in Canada will be able to carry firearms, and detain travelers who try to voluntarily withdraw their application. Although CBP does not have arrest powers in Canada the bill also includes increased cooperation with the Canada Border Services Agency to arrest travelers found to be breaking the law. 
On March 10, 2016, U.S. and Canadian officials announced that preclearance would become available at Billy Bishop Toronto City Airport, Québec City Jean Lesage International Airport, and Montreal Central Station. The necessary upgrades in Quebec City will take 18 months and $35 million CAD to complete.
On December 8, 2016, U.S. President Barack Obama signed the bipartisan Promoting Travel, Commerce and National Security Act of 2016 into law, enabling an expansion of US-Canada preclearance. On December 12th 2017, Canadian Governor General Julie Payette gave royal assent to the Canadian counterpart legislation: the Preclearance Act, 2016. The only hurdles standing in the way of implementing an expanded preclearance regime are orders-in-council (="executive order") in Canada, a joint agreement between President Donald Trump and Prime Minister Justin Trudeau, and an official presidential proclamation from Trump.
The following Canadian airports operate U.S. preclearance facilities:
At the request of Porter Airlines, a new terminal building at Billy Bishop Toronto City Airport (Toronto island) officially opened in Fall 2010 and includes both Canada Border Services Agency customs facilities and provisions for U.S. Customs and Border Protection border preclearance facilities. The latter was, however, denied by Washington at the time.
The airport security inspection in the US Departure area is before the Preclearance process, it was processed by Canadian Air Transport Security Authority (CATSA) and meet the standards of U.S. TSA regulations.
The United States operates a preclearance post at Pacific Central Station in Vancouver, British Columbia for Amtrak Cascades rail service connecting Vancouver to Seattle, Washington and Portland, Oregon.
In May 2012, U.S. Senators Charles Schumer, Kirsten Gillibrand, Patrick Leahy, and Bernie Sanders sent a letter to President Barack Obama urging him to fast track the approval of a preclearance facility in Montreal's Central Station, which will prevent U.S.-bound travelers from having to stop at the train station in Rouses Point, New York for immigration and customs checks whenever they cross the Canada-U.S. border. On March 16, 2015, the United States and Canada signed an agreement that would allow for such a facility.
The United States operates several immigration-only pre-inspection posts (customs is still performed upon arrival in the United States) at the port of Victoria for both the Black Ball Line MV Coho car ferry service to Port Angeles, Washington and the Victoria Clipper passenger-only ferry to Seattle, Washington; and at the terminal in Sidney for Washington State Ferries' Anacortes-San Juan Islands ferry service to Anacortes, Washington.
A U.S. preclearance post is also located at the Port of Vancouver. The latter is particularly valuable to travelers using cruise liners that visit Alaska or that depart from Vancouver and have a first stop at U.S. cities situated along the west coast of North America.
Plans were underway for a preclearance facility to be opened at Punta Cana International Airport, located in the popular tourist destination of Punta Cana, Dominican Republic by the end of summer 2009. Further plans were made in April 2016 to open a facility the next year but as of March 2018, however, the facility has not opened yet. In April 2011, a team from the U.S. Department of Homeland Security traveled to Jamaica for talks with Jamaican government and tourism officials on opening future preclearance facilities on the island.
The United States and Ireland entered into a preinspection arrangement in 1986.Shannon Airport initially offered only immigration checks, with customs and agriculture inspections done on arrival in the United States--a procedure more properly known as preinspection. In August 2009, Shannon opened an addition to its preclearance facility that provided customs and agriculture inspections. The facilities at Dublin Airport, like those at Shannon, initially offered only immigration checks on select flights. In January 2011, a section of the recently opened Terminal 2 dedicated to preclearance opened with full CBP facilities. Both airports now allow U.S.-bound commercial flights that use the preclearance facilities to arrive at domestic terminals instead of international terminals, which in turn allows arriving passengers to leave airports upon landing without further inspection. Since March 2010, the Shannon preclearance facility is also available for use by private aircraft; the Dublin facility is only available for commercial flights. Following Executive Order 13769, which introduced a ban on passport-holders of seven countries traveling to the United States, the Irish government announced that there would be a "complete review" of preclearance arrangements.
On June 6, 2013, the House passed an amendment offered by Representatives Pat Meehan (R-PA), Candice Miller (R-MI) and Peter DeFazio (D-OR), which prohibits the U.S. Department of Homeland Security (DHS) from using any taxpayer dollars to conduct customs and border protection (CBP) preclearance operations at Abu Dhabi International Airport (AUH). The amendment was unanimously adopted during floor consideration of the FY14 Homeland Security Appropriations bill.  On November 14, 2013, Rep. Patrick Meehan (R, PA-7) introduced the Preclearance Authorization Act of 2014 (H.R. 3488; 113th Congress), which would authorize the United States Secretary of Homeland Security (DHS) to establish preclearance facilities, conduct preclearance operations, or provide customs services outside of the United States to prevent terrorists, terrorist instruments, and other national security threats from gaining access to the United States. Meehan indicated that the goal of the bill is to prevent the Customs Bureau from opening a pre-clearance facility at Abu Dhabi International Airport in the United Arab Emirates. Currently just one airline flies from Abu Dhabi to the United States: Etihad, a state-run airline. Supporters of the bill wish to avoid giving Etihad an unfair competitive advantage created by travelers flying through that Abu Dhabi being able to use preclearance, an opportunity passengers on other airlines would not have. This bill did not pass into law.
The U.S. customs pre-clearance facility at Abu Dhabi International Airport officially opened on January 26, 2014. A U.S. customs preclearance facility is currently being planned for Dubai International Airport.
On March 16, 2015, the United States and Canada signed an agreement to construct a preclearance facility at Montreal Central Station. The facility will eliminate a border stop for Amtrak's Adirondack service and support a future extension of the Vermonter to Montreal.
In May 2015, the United States Department of Homeland Security announced that the following airports will be considered for the expansion of border preclearance scheme:
On November 4, 2016, Sweden and the United States signed an agreement that would make Sweden the second European country, after Ireland, to offer preclearance, although no announcement has been made as to when the service will start. November 4, 2016 was also the date of a DHS announcement that eleven more airports in nine countries had been added to the list of possible preclearance airports:
On 23 March 2018, the Taiwanese newspaper Liberty Times reported that the U.S. had conditionally agreed to the establishment of a border preclearance system in Taiwan. The Taiwanese government is assessing the possibility of establishing a United States border preclearance system at its main airport, and according to Ministry of Foreign Affairs (MOFA) spokesman Andrew Lee, the relevant government ministries are examining the issue and discussing how such a system can be put in place at Taiwan Taoyuan International Airport.
On 18 August, 2019, outgoing U.S. Ambassador to Colombia Kevin Whitaker stated that U.S. preclearance at El Dorado International Airport would be available within the next year, according to an interview with El Tiempo.
Ministry of Foreign Affairs of South Korea stated that the government of South Korea plans to establish the U.S. preclearance system at Incheon International Airport. On January 15, 2015, however, Incheon International Airport announced that it would not introduce the U.S. preclearance after an in-depth analysis concluded that U.S. preclearance could lead to decreased sales at duty-free shops, despite the potential income from usage fees remitted for the use of preclearance space.
On May 23, 2015, an unofficial member of the Executive Council of Hong Kong, Regina Ip, revealed in an interview that the United States and Hong Kong had explored the possibilities "some 20 or 30 years ago" to set up the preclearance arrangements at Kai Tak Airport. According to Ip, she was dispatched by the Secretary for Security, in her capacity as a career civil servant in the Security Branch, to study the arrangements in Canada, but the plan was subsequently shelved because of room constraints at Kai Tak.
On February 1, 2017, the Netherlands pulled out of talks with the United States to set up a pre-clearance program at Amsterdam Airport Schiphol because of U.S. President Donald Trump's Executive Order 13769, which banned travel to the United States by citizens of certain Muslim-majority countries. On 22 June 2018, the Dutch Government made it known that they were resuming plans for a pre-clearance facility at Amsterdam Airport Schiphol.
The Netherlands has also been in talks with the U.S. since December about extending pre-clearance to its Schiphol international airport, but on Tuesday it abruptly ended them.