Boeing Field, formally known as King County International Airport, is a large general aviation
(no scheduled carrier service) airport in Seattle
Its ICAO identifier is KBFI (since all ICAO airports in the US start with 'K' that letter is frequently omitted.) It is located at 47d31'47.961''N, 122d18'07.042''W, 18 feet MSL (WGS 84). It has two runways; 13R/31L is 10001x200' and 13L/31R is 3710x100'. It is a controlled field with class D airspace.
The field is a public-use airport, and is not restricted to Boeing, although Boeing has a large presence on the field and delivers many aircraft from it. Flying into BFI is an interesting experience as there are many aircraft operating alongside you which are not often seen elsewhere. There are usually several AWACS airplanes, 747s, 777s, alongside Piper Cubs, Cessnas and experimental aircraft.
Galvin Flying Service is widely recognized as the premier FBO (Fixed Base Operator) on the field, but it has many competitors.
BFI is an excellent but expensive place for flight training, charter flights, and other aeronautical pastimes. In addition, the Boeing Museum of Flight is located on the field (ramp tiedowns available, 24 hours PPR).
Airport specifications from FAA Flight Service Publications