The City of Aspen is a Home Rule Municipality that is the county seat and the most populous city of Pitkin County, Colorado, United States. The United States Census Bureau estimates that the city population was 5,804 in 2005. Founded as a mining camp in the Colorado Silver Boom and named because of the abundance of aspen trees in the area, the city is now a ski resort and an upscale tourist center. Aspen is located at 39° 11' 32"N 106° 49' 28"W (39.192297, -106.824470), along State Highway 82. According to the United States Census Bureau, the city has a total area of 3.5 square miles, all of it land.

In the late 20th century the city developed as an off-beat haven for celebrities, attracting such people as John Denver (who wrote several folk songs about the town, including "Aspenglow", and "Starwood in Aspen") Michael Douglas and Hunter S. Thompson.

The city sits along the southeast (upper) end of the Roaring Fork Valley, along the Roaring Fork River, a tributary of the Colorado River about 40 miles south of Glenwood Springs, Colorado. It is surrounded by mountain and wilderness areas on three sides: Red Mountain to the north, Smuggler Mountain to the east, and Aspen Mountain to the south.

The city's roots are traced to the winter of 1879, when a group of miners ignored pleas by Frederick Pitkin, governor of Colorado, to return across the Continental Divide due to an uprising of the Ute Indians. Originally named Ute City, the small community was renamed Aspen in 1880, and, in its peak production years of 1891 and 1892, surpassed Leadville as the United States' most productive silver-mining district. Production expanded due to the passage of the Sherman Silver Purchase Act of 1890, which doubled the government's purchase of silver. By 1893, Aspen had banks, a hospital, two theaters, an opera house and electric lights. Economic collapse came with the Panic of 1893, when President Cleveland called a special session of Congress and repealed the act. Within weeks, many of the Aspen mines were closed and thousands of miners were put out of work. It was proposed that silver be recognized as legal tender and the Populist Party adopted that as one of its main issues; Davis H. Waite, an Aspen newspaperman and agitator was elected governor of Colorado on the Democratic Ticket; but in time the movement failed.

Eventually, after wage cuts, mining revived somewhat, but production declined and by the 1930 census only 705 residents remained. There was a fine stock of old business blocks and residences and excellent snow. Aspen's development as a ski resort first flickered in the 1930s when investors conceived of a ski area, but the project was interrupted by World War II. Friedl Pfeifer, a member of the 10th Mountain Division who had trained in the area, returned to the area and linked up with industrialist Walter Paepcke and his wife Elizabeth. The Aspen Skiing Corporation was founded in 1946 and the town quickly became a well-known resort, hosting the FIS World Championships in 1950. Paepcke also played an important role in bringing the Goethe Bicentennial Convocation to Aspen in 1949, an event held in a newly designed tent by the architect Eero Saarinen. Aspen was now on the path to becoming an internationally known ski resort and cultural center, home of the Aspen Music Festival and School. The area would continue to grow with the development of three additional ski areas, Buttermilk (1958), Aspen Highlands(1958), and Snowmass (1969).

In 1977, Aspen was thoroughly photographed for the Aspen Movie Map project funded by the U.S. Department of Defense. The Movie Map is one of the earliest examples of virtual reality software.

Aspen is notable as the smallest radio market tracked by Arbitron, ranked at #302.