Tucson (pronounced /ˈtusɑn/) is a city and the county seat of Pima County, Arizona, United States, located 118 miles (188 km) southeast of Phoenix. As of July 1, 2004 a Census estimate put the city's population at 521,605, and the metropolitan population at 931,210. The population of metropolitan Tucson is expected to exceed 1 million by spring 2007. Also by 2008 the city population is expected to exceed 610,000 residents. In 2004 Tucson ranked as the 32nd largest city, and 55th largest metropolitan area in the U.S. It is the largest city in southern Arizona, and the second largest in the state after Phoenix. Two United States Navy ships have also been named USS Tucson in honor of the city.

Major incorporated suburbs of Tucson include Oro Valley and Marana northwest of the city, and South Tucson and Sahuarita south of the city. Other communities near Tucson include Casas Adobes, Catalina, Catalina Foothills, Flowing Wells, Green Valley, Tanque Verde, and Vail.

The name Tucson comes via Spanish from the O'odham, Cuk Ṣon (pronounced [ʧʊk ʂɔn]; roughly, "chuk shon"), meaning "Black Base," a reference to the mostly volcanic mountains on the west side of the city. The most notable of these foothills is Sentinel Peak, better known as "A Mountain" because it sports a large letter A in honor of the nearby University of Arizona, situated in west central Tucson. Tucson is sometimes referred to as "The Old Pueblo." A contest in the 1980s to coin a new nickname produced "The Sunshine Factory," which Tucsonans ignored in favor of the original.