Seattle-Tacoma International Airport opened on October 31, 1944, built by the Port of Seattle on a plateau near Bow Lake, roughly midway between Seattle and Tacoma, after the U.S. military commandeered Boeing Field during World War II. The first scheduled commercial flights began on September 1, 1947, with Northwest Airlines and Western Airlines operating ten daily departures. The terminal was formally dedicated by Governor Arthur Langlie on July 9, 1949, in front of a crowd of 30,000. It was a 71,000-square-foot building designed by architect Herman A. Moldenhour, with a rooftop control tower and glass curtain walls in the concourses, hailed at the time as America's most advanced airport terminal.

Geographically, SEA sits 14 miles south of downtown Seattle in the city of SeaTac, a municipality named after the airport's own nickname. It is the busiest airport in the Pacific Northwest. The airport is the primary hub for Alaska Airlines, whose headquarters are located nearby, and a major hub and international gateway for Delta Air Lines, which expanded its presence significantly from 2011 onward. As of 2026, 37 airlines serve the airport, connecting 96 domestic and 37 international destinations across North America, Asia, Europe, the Middle East, and Oceania.

SEA operates 3 parallel north-south runways. The third runway opened on November 20, 2008, after more than 20 years of planning and over $1 billion in construction costs, and was designed to enable simultaneous landings during low-visibility conditions. In 2022, the airport completed a $968 million International Arrivals Facility featuring a 780-foot glass-enclosed aerial walkway suspended 85 feet above an active taxiway, the longest such structure over an active taxilane in the world. In 2025, the airport set an all-time passenger record with 52,715,181 travelers served.