The International Ladies' Garment Workers' Union was once one of the largest labor unions in the United States founded in 1900 by local union delegates representing about 2,000 members in cities in the northeastern United States. It was one of the first U.S. Unions to have a membership consisting of mostly females, and it played a key role in the labor history of the 1920s and 1930s. The union is generally referred to as the "ILGWU" or the "ILG". The ILGWU grew in geographical scope, membership size, and political influence to become one of the most powerful forces in American organized labor by mid-century. Representing workers in the women's garment industry, the ILGWU worked to improve working and living conditions of its members through collective bargaining agreements, training programs, health care facilities, cooperative housing, educational opportunities, and other efforts. The ILGWU merged with the Amalgamated Clothing and Textile Workers Union in 1995 to form the Union of Needle trades, Industrial and Textile Employees (UNITE). UNITE merged with the Hotel Employees and Restaurant Employees Union (HERE) in 2004 to create a new union known as UNITE HERE. The two unions that formed UNITE in 1995 represented only 250,000 workers between them, down from the ILGWU's peak membership of 450,000 in 1969.

Local 155, International Ladies' Garment Workers' Union ILGWU), also known as the Knitgoods Workers' Union, was chartered in 1933 and based in New York City.