The Lower East Side, sometimes abbreviated as LES, is an historic neighborhood in the southeastern part of Manhattan in New York City. It is located roughly between the Bowery and the East River from Canal to Houston streets. Historically, it was understood to encompass a much larger area, from Broadway to the East River and from East 14th Street to Fulton and Franklin Streets.

Traditionally an immigrant, working class neighborhood, it began rapid gentrification in the mid-2000s, prompting the National Trust for Historic Preservation to place the neighborhood on their list of America's Most Endangered Places in 2008.

The Lower East Side is part of Manhattan Community District 3, and its primary ZIP Code is 10002. It is patrolled by the 7th Precinct of the New York City Police Department.

The Lower East Side is roughly bounded by East 14th Street on the north, by the East River to the east, by Fulton and Franklin Streets to the south, and by Pearl Street and Broadway to the west. This more extensive definition of the neighborhood includes Chinatown, the East Village, and Little Italy. A less extensive definition would have the neighborhood bordered in the south and west by Chinatown, – which extends north to roughly Grand Street – in the west by Nolita and in the north by the East Village.

Historically, the "Lower East Side" referred to the area alongside the East River from about the Manhattan Bridge and Canal Street up to 14th Street, and roughly bounded on the west by Broadway. It included areas known today as East Village, Alphabet City, Chinatown, Bowery, Little Italy, and NoLIta. Parts of the East Village are still known as Loisaida, a Latino pronunciation of "Lower East Side".

Politically, the neighborhood is in New York's 7th and 12th congressional districts. It is in the New York State Assembly's 65th district and 74th district; the New York State Senate's 26th district; and New York City Council's 1st and 2nd districts.

As was true of all of Manhattan Island, the area now known as the Lower East Side was occupied by members of the Lenape tribe, who were organized in bands that moved from place to place according to the seasons, fishing on the rivers in the summer, and moving inland in the fall and winter to gather crops and hunt for food. Their main trail took approximately the route of Broadway. One encampment on the Lower East Side near Corlears Hook was called Rechtauck or Naghtogack.

The population of the Dutch colony of New Amsterdam was located primarily below the current Fulton Street, while north of it were a number of small plantations and large farms called "bouwerij" ("bowery", equivalent to "boerderij" in present-day Dutch). Around these farms were a number of enclaves of free or "half-free" Africans, which served as a buffer between the Dutch and the Native Americans. One of the largest of these was located along the modern Bowery between Prince Street and Astor Place, as well as the "only separate enclave" of this type within Manhattan. These black farmers were some of the earliest settlers of the area.