The Fort Selden State Monument is a monument and historic site in Radium Springs, New Mexico. The site was originally a military outpost created in 1865 as Fort Selden. It was established to protect settlers from the raids of the Native Americans.

Fort Selden served its purpose for a couple of years, but was eventually abandoned after the Civil War. It was totally left behind in 1891, when the nearby Fort Bliss was expanded instead. For some time, the old fort was left to the harsh outdoor conditions, as well as to the mercy of vandals, souvenir hunters, and treasure seekers. It was reduced to ruins until in 1963, a local decided to donate the land to the state.

Fort Selden State Monument was eventually listed on the National Register of Historic Places in 1970 and then became a state monument four years later. It now has a museum and an interpretive trail on the site. Living history demonstrations are also regularly held here as well.