Arizona is a state in the Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the northwest and California to the west, and shares an international border with the Mexican states of Sonora and Baja California to the south and southwest. Its capital and largest city is Phoenix, which is the most populous state capital and fifth most populous city in the United States. Arizona is divided into 15 counties.

Arizona is the 6th-largest state by area and the 14th-most-populous of the 50 states. It is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of Alta California and Nuevo México in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848, where the area became part of the New Mexico Territory. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.

Southern Arizona is known for its desert climate, with extremely hot summers and mild winters.