Whether you must go through security for a connecting flight in 2026 depends on your origin and destination. If you are connecting from one domestic flight to another within the same terminal (or a connected terminal) in countries like the U.S., you typically stay "airside" and do not go through security again. However, if you are arriving on an international flight and connecting to a domestic one, you almost always have to clear customs, collect your bags, and then go through a TSA or local security checkpoint before entering the domestic departures area. This is true for almost all arrivals into the U.S. and UK. In the European Schengen Area, if you arrive from a non-Schengen country (like the U.S.) and connect to a Schengen destination (like Paris to Berlin), you will clear passport control and often a security screen. Some modern airports have "clean" transit corridors for passengers from "trusted" countries that allow you to skip the re-screening, but this varies by specific airport agreements and is not yet a global standard in 2026.