Arizona ( (listen) ARR-iz-OH-nə; Navajo: Hoozdo Hahoodzo Navajo pronunciation: [hoː˥z̥to˩ ha˩hoː˩tso˩]; O'odham: Alĭ ṣonak) is a state in the Western United States, grouped in the Southwestern and occasionally Mountain subregions. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona shares the Four Corners region with Utah to the north, Colorado to the northeast, and New Mexico to the east; its other neighboring states are Nevada to the northwest and California to the west and the Mexican states of Sonora and Baja California to the south and southwest.

Arizona 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 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. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.

Southern Arizona is known for its desert climate, with very hot summers and mild winters. Northern Arizona features forests of pine, Douglas fir, and spruce trees; the Colorado Plateau; mountain ranges (such as the San Francisco Mountains); as well as large, deep canyons, with much more moderate summer temperatures and significant winter snowfalls. There are ski resorts in the areas of Flagstaff, Alpine, and Tucson. In addition to the internationally known Grand Canyon National Park, which is one of the world's seven natural wonders, there are several national forests, national parks, and national monuments.

Since the 1950s, Arizona's population and economy have grown dramatically because of migration into the state, and now the state is a major hub of the Sun Belt. Cities such as Phoenix and Tucson have developed large, sprawling suburban areas. Many large companies, such as PetSmart and Circle K, have headquarters in the state, and Arizona is home to major universities, including the University of Arizona and Arizona State University. Traditionally, the state is politically known for national conservative figures such as Barry Goldwater and John McCain, though it voted Democratic in the 1996 presidential race and in the 2020 presidential and senatorial elections.

Arizona is home to a diverse population. About one-quarter of the state is made up of Indian reservations that serve as the home of 27 federally recognized Native American tribes, including the Navajo Nation, the largest in the state and the United States, with more than 300,000 citizens. Since the 1980s, the proportion of Hispanics in the state's population has grown significantly owing to migration from Mexico. In terms of religion, a substantial portion of the population are followers of the Catholic Church and The Church of Jesus Christ of Latter-day Saints (LDS Church).