first important national labour organization in the United States, founded in 1869. Named the Noble Order of the Knights of Labor by its first leader, Uriah S. Stephens (Stephens, Uriah Smith), it originated as a secret organization meant to protect its members from employer retaliations. Secrecy also gave the organization an emotional appeal.

The organization's original platform was partly ideological; based on a belief in the unity of interest of all producing groups (shopkeepers and farmers, as well as labourers), it proposed a system of worker cooperatives to replace capitalism. After the election of Terence V. Powderly (Powderly, Terence V.) as grand master workman of the national organization in 1879, the group abandoned its secrecy and mystical trappings and struck the word noble from its title. Because Powderly was unwilling to initiate strikes or use other forms of economic pressure to gain the union's objectives, effective control of the organization shifted to regional leaders. Membership in the Knights grew after the railway strike in 1877, reaching a peak of 700,000 in 1886. At that time the Knights were the dominant labour organization in the United States.

The KOL's influence declined sharply after 1886—a year marked by 1,600 strikes (some of them violent) and the deadly Haymarket Riot in Chicago. The resulting backlash against unionism, along with the dissatisfaction of many KOL members, led to the union's demise and fostered the establishment of the American Federation of Labor (American Federation of Labor–Congress of Industrial Organizations) (AFL) in December 1886. The AFL focused on winning economic benefits for its members through collective bargaining. As a federation, it represented several national craft unions that each retained autonomous operations. The Knights, by contrast, represented both craft and unskilled workers in a single national union.