Preclearance programs have been accused of being motivated by a desire to prevent the arrival of asylum seekers, who are otherwise protected under the 1951 Refugee Convention's provisions on non-refoulement once they arrive at their destination.

airports without customs facilities for processing commercial flights. airports have expanded or introduced customs facilities since the preclearance program began, LaGuardia Airport and Ronald Reagan Washington National Airport remain the two largest U.S. airports that may not be equipped to otherwise handle international travelers. The preclearance program aims to streamline border procedures for flights entering the United States, reduce congestion at ports of entry, and to facilitate travel into U.S. Preclearance facilities also exist in airports in Aruba, the Bahamas, Bermuda, Ireland, and the United Arab Emirates. Modern preclearance facilities were first introduced in 1952 at Malton Airport (now Toronto Pearson International Airport) and Calgary International Airport under an informal arrangement with the government of Canada and are now available at eight major Canadian airports and one seaport, while several other seaports and one rail station in British Columbia have 'pre-inspection' facilities for screening immigration admissibility only.

The history of inspecting U.S.-bound passengers in foreign countries began in 1894, when American immigration inspectors were deployed to sea ports in Canada. This process is intended to streamline border procedures, reduce congestion at American ports of entry, and facilitate travel into airports that otherwise lack immigration and customs processing facilities for commercial flights. Upon arrival, precleared passengers arrive in the United States as domestic travelers, but may still be subject to re-inspection at the discretion of CBP. Preclearance applies to all passengers regardless of their nationality or purpose of travel. Travelers are subject to immigration and customs inspections by Customs and Border Protection (CBP) officers before boarding their transportation onward to the United States.

Preclearance is the United States Department of Homeland Security's (DHS) practice of operating prescreening border control facilities at airports and other ports of departure located outside of the United States pursuant to agreements between the United States and host countries. A preclearance booth at Shannon Airport in 2008.

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