Marble House is a Gilded Age mansion in Newport, Rhode Island. Designed as a summer cottage for Alva and William Kissam Vanderbilt by the society architect Richard Morris Hunt, it was unparalleled in opulence for an American house when it was completed in 1892. Its temple-front portico, which also serves as a porte-cochère, resembles that of the White House. Located at 596 Bellevue Avenue, it is now open to the public as a museum run by the Preservation Society of Newport County.

The mansion was built as a summer "cottage" between 1888 and 1892 for Alva and William Kissam Vanderbilt. It was a social landmark that helped spark the transformation of Newport from a relatively relaxed summer colony of wooden houses to the now-legendary resort of opulent stone palaces. The fifty-room mansion required a staff of 36 servants, including butlers, maids, coachmen, and footmen. The mansion cost $11 million (equivalent to $307 million in 2018; $660 million in Gold-dollar equivalence (1890 $20 Double Eagle)) of which $7 million was spent on 500,000 cubic feet (14,000 m³) of marble. Vanderbilt's older brother Cornelius Vanderbilt II subsequently built the largest of the Newport cottages, The Breakers, between 1893 and 1895.

When Alva Vanderbilt divorced William in 1895, she already owned Marble House outright, having received it as her 39th birthday present. Upon her remarriage in 1896 to Oliver Hazard Perry Belmont, she relocated down the street to Belmont's mansion, Belcourt. After his death, she reopened Marble House and added the Chinese Tea House on the seaside cliff, where she hosted rallies for women's suffrage.

Alva Belmont closed the mansion permanently in 1919, when she relocated to France to be closer to her daughter, Consuelo Balsan. There she divided her time between a Paris townhouse, a villa on the Riviera, and the Château d'Augerville, which she restored. She sold the house to Frederick H. Prince in 1932, less than a year before her death. For more than 30 years, the Prince family carefully occupied the house during Newport's summer season, taking special efforts to leave the vast majority of the interior intact as the Vanderbilts had originally intended. One notable event that occurred in the Marble House during the Prince family's residency was the famed Tiffany Ball in July 1957, sponsored by Tiffany & Company and held to benefit the relatively new Preservation Society of Newport County. Continuing late into the early morning hours, the ball welcomed guests with long national and international pedigrees, such as then Senator John F. Kennedy and his wife, Jacqueline Bouvier Kennedy; Mr. and Mrs. E. Sheldon Whitehouse; the Astors; Count Anthony and Countess Sylvia Szapary of the Vanderbilt family; and hundreds of other luminaries. During their summer occupancies, to help preserve the integrity of Marble House's famed interiors, the Princes primarily resided in smaller quarters in the building's third floor, which had formerly been used for servant housing during the Vanderbilts' time. In 1963, the Preservation Society of Newport County purchased the house from the Prince Trust, with funding provided by Harold Stirling Vanderbilt, the Vanderbilt couple's youngest son. Through the Prince Trust, the Prince family donated virtually all original furniture for the house directly to the Preservation Society.

The mansion was added to the National Register of Historic Places on September 10, 1971. The Department of the Interior designated it as a National Historic Landmark on February 17, 2006. The Bellevue Avenue Historic District, which includes Marble House and many other historic Newport mansions, was added to the Register on December 8, 1972 and subsequently designated as a National Historic Landmark District on May 11, 1976. The mansion still stands in great visible condition and is used for many things such as guided and non-guided tours, as well as hosting various special events, parties, and weddings.