Portland International Airport opened on October 13, 1940, on a stretch of Columbia River floodplain in northeast Portland. Originally called Portland-Columbia Airport, it replaced the city's first airfield at Swan Island, which had operated since 1927. The site required 4 million cubic yards of dredged fill to make it usable, funded through a $300,000 city bond and a $1.3 million Works Progress Administration grant. Just 8 years after opening, the 1948 Columbia River flood inundated the airport grounds, one of the most destructive flood events in Pacific Northwest history.

The airport grew steadily through the postwar decades. A new terminal opened between 2 long parallel runways in 1959, establishing the layout that persists today. The IATA code PDX was assigned after World War II by appending X to the existing 2-letter National Weather Service identifier, the same method used by Los Angeles and Phoenix. PDX is the primary airport in Oregon, handling roughly 90% of the state's passenger air travel. It is a hub for Alaska Airlines and connects the region to destinations across North America, Europe, and beyond through a single compact terminal with 4 concourses.

The airport's most significant recent transformation was the $2 billion PDXNext redevelopment. Phase 1 opened in August 2024, introducing a 9-acre mass-timber roof, the largest mass-timber structure of its kind, sourced from forests within 300 miles of the airport. The MAX Red Line light rail, which began direct service to the terminal in September 2001, connects the airport to downtown Portland in roughly 38 minutes. PDX sits 6 miles northeast of downtown by air, bounded by the Columbia River to the north and the Columbia Slough to the south.