The Congress of Industrial Organizations (CIO) was a federation of unions in the United States, established in 1935. It aimed to organize workers in mass production industries, such as steel and automobiles, to improve labor rights and conditions. The CIO played a significant role in advocating for workers' rights during the Great Depression. In 1955, the CIO merged with the American Federation of Labor (AFL) to form the AFL-CIO, creating a larger and more powerful labor organization. The CIO's focus on industrial unionism helped to increase membership and influence in the labor movement, shaping the landscape of American labor relations.