Lajes Field or Lajes Air Base, officially designated Air Base No. 4, is a multi-use airfield near Lajes and 15 km (9.3 mi) northeast of Angra do Heroísmo on Terceira Island in the Azores, Portugal. It is home to the Portuguese Air Force Base Aérea N º4 and Azores Air Zone Command, a United States Air Force detachment unit, and a regional air passenger terminal. Located about 3,680 km (2,290 mi) east of New York City and about 1,600 km (990 mi) west of Lisbon, Portugal; the base sits in a strategic location midway between North America and Europe in the north Atlantic Ocean.

Terceira is a volcanic island in the Azores archipelago, about a third of the way across the North Atlantic Ocean at a similar latitude to Portugal's capital Lisbon, and the island group is an insular part of Portugal. It is one of the larger islands of the archipelago, with a population of 53,311 inhabitants in an area of approximately 396.75 km².