The American Federation of Labor and Congress of Industrial Organizations, commonly AFL–CIO, is a national trade union center

National trade union center

A national trade union center is a federation or confederation of trade unions in a single country. Nearly every country in the world has a national trade union center, and many have more than one. When there is more than one national center, it is often because of ideological differences—in some...

, the largest federation of unions

Labor unions in the United States

Labor unions in the United States are legally recognized as representatives of workers in many industries. The most prominent unions are among public sector employees such as teachers and police...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, made up of 56 national and international unions, together representing more than 11 million workers (as of June 2008, the most recent official statistic). It was formed in 1955 when the AFL

American Federation of Labor

The American Federation of Labor was one of the first federations of labor unions in the United States. It was founded in 1886 by an alliance of craft unions disaffected from the Knights of Labor, a national labor association. Samuel Gompers was elected president of the Federation at its...

 and the CIO

Congress of Industrial Organizations

The Congress of Industrial Organizations, or CIO, proposed by John L. Lewis in 1932, was a federation of unions that organized workers in industrial unions in the United States and Canada from 1935 to 1955. The Taft-Hartley Act of 1947 required union leaders to swear that they were not...

 merged after a long estrangement. From 1955 until 2005, the AFL–CIO's member unions represented nearly all unionized workers in the United States.