St. Louis Lambert International Airport is the primary commercial airport serving metropolitan St. Louis, Missouri, United States. Commonly referred to as Lambert Field or simply Lambert, it is the largest and busiest airport in the state of Missouri. The airport covers 3,793 acres (1,535 ha) of land. STL is located 14 miles (23 km) northwest of downtown St. Louis in unincorporated St. Louis County between Berkeley and Bridgeton. The airport provides nonstop service to airports throughout the United States and to the Caribbean, Mexico, Canada, and Europe. In 2019, it served nearly 16 million passengers. In 2023 there were more than 270 daily departures to 80 nonstop domestic and international locations.

Greater St. Louis is the 21st-largest metropolitan statistical area (MSA) in the United States, the largest in Missouri, and the second-largest in Illinois. Its core city—St. Louis, Missouri—sits in the geographic center of the metro area, on the west bank of the Mississippi River. The river bisects the metro area geographically between Illinois and Missouri, although the latter portion is much more populous. The MSA includes St. Louis County, which is independent of the City of St. Louis; their two populations are generally tabulated separately.