Glenstone is a private contemporary art museum in Potomac, Maryland, from downtown Washington, D.C. The museum's exhibitions are drawn from a collection of about 1,300 works from post-World War II artists around the world. It is the largest private contemporary art museum in the United States and is noted for its setting in a broad natural landscape. The museum was developed and financed by billionaire American businessman Mitchell Rales and is curated by Emily Wei Rales. Artists in Glenstone's collection must have already been exhibited for at least 15 years. First opened in 2006 in a building designed by Charles Gwathmey, the museum has been expanded several times between 2013 and 2018 on its campus. Its most significant expansion was opened to the public on October 4, 2018, with outdoor sculpture installations, landscaping, and the introduction of a new museum complex called the Pavilions designed by Thomas Phifer. In 2019, Glenstone added an environmental center with exhibits on recycling, composting, and reforestation. Glenstone has been compared to other private museums, such as the Frick Collection and The Phillips Collection, and has received generally positive reviews in the press. The museum is open, free to the public, via online booking. History In 1986, billionaire American businessman Mitchell Rales purchased the property in Potomac, Maryland, to build a home. Starting in 1990, Rales began collecting art for that home. Following a near-death accident on a helicopter trip in Russia, Rales decided to take on a philanthropic project, which became the establishment of a private contemporary art museum. Built on land that was formerly a fox hunting club, Glenstone is named for the nearby Glen Road, and because of stone quarries located in the vicinity. Located from downtown Washington, D.C., the museum's initial Modernist limestone gallery opened in 2006 and admitted visitors two days a week. In its first seven years, the museum admitted only 10,000 visitors.Though several smaller expansions took place in the years after the museum's opening, the largest expansion was announced in 2013 and was completed in 2018, opening to the public on October 4, 2018. With a cost of approximately $219 million, the expansion increased the size of the museum's gallery space by a factor of five, increasing the property's size by , and included substantial landscaping changes. With the expansion, Glenstone became the largest private contemporary art museum in the United States. In 2019, the expansion was named