Alamogordo (/ˌæləməˈɡɔːrdoʊ/) is a city in and the county seat of Otero County, New Mexico, United States. A city in the Tularosa Basin of the Chihuahuan Desert, it is bordered on the east by the Sacramento Mountains and to the west by Holloman Air Force Base. The population was 31,384 as of the 2020 census. Alamogordo is widely known for its connection with the 1945 Trinity test, which was the first-ever explosion of an atomic bomb.

Humans have lived in the Alamogordo area for at least 11,000 years. The present settlement, established in 1898 to support the construction of the El Paso and Northeastern Railroad, is an early example of a planned community. The city was incorporated in 1912. Tourism became an important economic factor with the creation of White Sands National Park in 1933, which is still one of the biggest attractions of the city today. During the 1950s and 1960s, Alamogordo was an unofficial center for research on pilot safety and the development of the United States' space program.

Alamogordo is a charter city with a council-manager form of government. City government provides a large number of recreational and leisure facilities for its citizens, including a large park in the center of the city, many smaller parks scattered through the city, a golf course, Alameda Park Zoo, a network of walking paths, Alamogordo Public Library, and a senior citizens' center. Gerald Champion Regional Medical Center is a nonprofit shared military/civilian facility that is also the hospital for Holloman Air Force Base.

Tularosa Basin has been inhabited for at least 11,000 years. There are signs of previous inhabitants in the area such as the Clovis culture, the Folsom culture, the peoples of the Archaic period, and the Formative stage. The Mescalero Apache were already living in the Tularosa Basin when the Spanish came in 1534, and Mescalero oral history says they have always lived there. In 1719, the Spanish built a chapel at La Luz (about 5 miles (8.0 km) from the future site of Alamogordo), although La Luz was not settled until about 1860.

The city of Alamogordo was founded in June 1898, when the El Paso and Northeastern Railroad, headed by Charles Bishop Eddy, extended the railway to the town. Eddy influenced the design of the community, which included large, wide thoroughfares and tree-lined irrigation canals. Charles Eddy's brother, John Arthur Eddy, named the new city. He created a neologism adapted from the Spanish words for "large/fat cottonwood" after a grove of stout cottonwoods he remembered from the Pecos River area. However, the word "Alamogordo" was not used in the Spanish language. When Alamogordo was laid out in 1898, the east–west streets were given numerical designations, while north–south streets were named after states. The present-day White Sands Boulevard was then called Pennsylvania Avenue.

With the creation of White Sands National Monument in 1934, tourism began.

The Works Progress Administration, a government program created in 1935 in response to the Great Depression, was responsible for the construction of several government buildings in Alamogordo. These include the Otero County Administration Building at 1101 New York Avenue, a Pueblo style building originally constructed as the main U.S. Post Office in 1938. The building is listed in the National Register of Historic Places. The main entrance portico features frescoes by Peter Hurd, which were completed in 1942.

In July 1941, the Alamogordo Bombing and Gunnery Range was established.