The Knights of Labor, officially the Noble and Holy Order of the Knights of Labor, was an American labor federation that was active in the late 19th century, especially the 1880s. It operated in the United States as well in Canada, and had chapters also in Great Britain and Australia. Its most important leader was Terence V. Powderly. The Knights of Labor promoted the social and cultural uplift of the worker, and demanded the eight-hour day. In some cases it acted as a labor union, negotiating with employers, but it was never well organized or funded. It was notable in its ambition to organize across lines of gender and race and in the inclusion of both skilled and unskilled labor. After a rapid expansion in the mid-1880s, it suddenly lost its new members and became a small operation again. The Knights of Labor had served, however, as the first mass organization of the white working class of the United States.

Labor federation competition in the United States is a history of the labor movement, considering U.S. labor organizations and federations that have been regional, national, or international in scope, and that have united organizations of disparate groups of workers. Union philosophy and ideology changed from one period to another, conflicting at times. Government actions have controlled, or legislated against particular industrial actions or labor entities, resulting in the diminishing of one labor federation entity or the advance of another.