The Upper East Side is a neighborhood in the borough of Manhattan in New York City, between Central Park and the East River.
Once known as the 'Silk Stocking District', it has some of the most expensive real estate in the United States. The most expensive Upper East Side penthouse (in The Pierre Hotel) was listed in the classifieds for approximately $70 million, and the most expensive townhouse was listed for $75 million.
Before the Park Avenue railroad cut was covered (finished in 1910), fashionable New Yorkers shunned the smoky railroad trench up Fourth Avenue (now Park Avenue), to build stylish mansions and townhouses on the large lots along Fifth Avenue, facing Central Park, and on the adjacent side streets, north of the Vanderbilt family's favored stretch of Fifth Avenue in the 50s. The latest arrivals were the rich Pittsburghers Andrew Carnegie and Henry Clay Frick. The first apartment house to replace a private mansion on upper Fifth Avenue was 907 Fifth Avenue (1916), at 72nd Street, the neighborhood's grand carriage entrance to Central Park.
Most members of New York's upper-class families have made residences on the Upper East Side, including the oil-rich Rockefellers
, political Roosevelts
, political dynastic Kennedys
, thoroughbred racing moneyed Whitneys
, and tobacco and electric power fortuned Dukes. 
Construction of the 3rd Avenue El, opened from 1878 in sections, followed by the 2nd Avenuel El, linked the Upper East Side's middle class and skilled artisans closely to the heart of the city. From the 1880s Yorkville, as it was known, extended east past Lexington Avenue and became a suburb of middle-class Germans, many of whom worked in nearby piano factories, stables, and breweries.
Gracie Mansion, the last remaining suburban villa overlooking the East River, became the home of New York's mayor in 1942.
The Upper East Side stretches from 59th Street to 96th Street (in the zip codes of 10021, 10022, 10065, 10075, 10028 and 10128). Along 5th Avenue and Central Park, the Upper East Side actually extends past Mount Sinai Medical Center to around 110th Street, but as you move East toward the East River, the Upper East Side technically ends at 97th Street. Embedded within the Upper East Side are the neighborhoods of Yorkville, centered on 86th Street and Third Avenue and Carnegie Hill, centered on 94th Street and Fifth Avenue and Lenox Hill centered on 69th Street and 1st Avenue.
Its north-south avenues are Fifth Avenue, Madison Avenue, Park Avenue, Lexington Avenue, Third, Second and First Avenues, York Avenue, and East End Avenue (the latter runs only from East 79th Street to East 90th Street).
Given its very high population density and per capita income ($85,081 in 2000), the neighborhood is believed to be the greatest concentration of individual wealth in the nation. As of 2000, 75.6% of adults (25+) had attained a bachelor's degree or higher.
The Upper East Side is also notable as a significant location of political fundraising in the United States. Four of the top five zip codes in the nation for political contributions are in Manhattan. The top ZIP Code, 10021, is on the Upper East Side and generated the most money for the 2004 presidential campaigns of both George W. Bush and John Kerry.
The area is host to some of the most famous museums in the world. The string of museums along Fifth Avenue fronting Central Park has been dubbed "Museum Mile." It was once named "Millionaire's Row." Among the cultural institutions on the Upper East Side:
The Upper East Side is also the location of Sutton Place, Manhattan Sutton Place. It is the site of a four-story townhouse built for Anne Morgan, daughter of financier J. P. Morgan, and now the official residence of the United Nations Secretary-General.