Tucson is a city in the US state of Arizona. It also serves as the seat of Pina County and is called by several nicknames including: The Old Peublo, Optics Valley, and the Sunshine Factory. With a population of over 1 million in its metropolitan area, the city was ranked as the 52nd largest metropolitan area in the United States in 2005. It is also the location of the University of Arizona.

Most of the city's economic development centers on the University of Arizona. It is also currently the second largest employer in the city. The University, together with the Davis-Monthan Air Force Base and the US Army Intelligence Center, the University has helped Tucson to have one of the leading high-tech industries in the United States. Around 150 companies in the city are involved in the designing and manufacture of optoelectronics and optics, giving the city the nickname: Optics Valley. The city also plays host to over 3.5 million American and foreign visitors annually.

Transportation to, from, and in and around the city are handled by the airport, railway and the local transit services. Tucson international sister cities include County Roscommon (Ireland), Almaty (Kazakhstan), Pecs (Hungary), Taichung City (Taiwan)m, and Trikala (Greece).