At Dulles Airport (IAD), passengers typically do not have to go through security again for a connecting flight, provided both flights are within the same concourse. However, if your connecting flight requires you to change concourses, you will likely need to go through security again. It is important to check with your airline or consult the airport staff for specific guidance based on your itinerary. In some cases, passengers may also need to clear security again if they are arriving on an international flight and connecting to a domestic flight.